tag:blogger.com,1999:blog-841209049800247432024-03-13T12:02:07.854-07:00astro-ph.GA : Galaxy AstrophysicsSite for <a href="http://communitypeerreview.blogspot.com/">Community Peer Review</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.comBlogger4187125tag:blogger.com,1999:blog-84120904980024743.post-86807433634511774012013-08-06T00:05:00.007-07:002013-08-06T00:05:03.403-07:001305.2405 (R. Agnese et al.)<h2 class="title"><a href="http://arxiv.org/abs/1305.2405">Demonstration of Surface Electron Rejection with Interleaved Germanium
Detectors for Dark Matter Search</a> [<a href="http://arxiv.org/pdf/1305.2405">PDF</a>]</h2>R. Agnese, A. J. Anderson, D. Balakishiyeva, R. Basu Thakur, D. A. Bauer, A. Borgland, D. Brandt, P. L. Brink, R. Bunker, B. Cabrera, D. O. Caldwell, D. G. Cerdeno, H. Chagani, M. Cherry, J. Cooley, B. Cornell, C. H. Crewdson, P. Cushman, M. Daal, P. C. F. Di Stefano, E. Do Couto E Silva, T. Doughty, L. Esteban, S. Fallows, E. Figueroa-Feliciano, J. Fox, M. Fritts, G. L. Godfrey, S. R. Golwala, J. Hall, H. R. Harris, J. Hasi, S. A. Hertel, B. A. Hines, T. Hofer, D. Holmgren, L. Hsu, M. E. Huber, A. Jastram, O. Kamaev, B. Kara, M. H. Kelsey, S. A. Kenany, A. Kennedy, C. J. Kenney, M. Kiveni, K. Koch, B. Loer, E. Lopez Asamar, R. Mahapatra, V. Mandic, C. Martinez, K. A. McCarthy, N. Mirabolfathi, R. A. Moffatt, D. C. Moore, P. Nadeau, R. H. Nelson, L. Novak, K. Page, R. Partridge, M. Pepin, A. Phipps, K. Prasad, M. Pyle, H. Qiu, R. Radpour, W. Rau, P. Redl, A. Reisetter, R. W. Resch, Y. Ricci, T. Saab, B. Sadoulet, J. Sander, R. Schmitt, K. Schneck, R. W. Schnee, S. Scorza, D. Seitz, B. Serfass, B. Shank, D. Speller, A. Tomada, A. N. Villano, B. Welliver, D. H. Wright, S. Yellin, J. J. Yen, B. A. Young, J. Zhang<a name='more'></a><blockquote class="abstract">SuperCDMS, a direct search for WIMPs, is currently operating a 9-kg array of cryogenic germanium (Ge) detectors in the Soudan Underground Laboratory. These detectors, known as iZIPs, use ionization and phonon sensors placed symmetrically on both sides of a Ge crystal to measure both charge and athermal phonons from each particle interaction. The information from each event provides excellent discrimination between electron recoils and nuclear recoils, as well as discrimination between events on the detector surface and those in the interior. To demonstrate the surface electron rejection capabilities, two $^{210}$Pb sources were installed facing detectors, producing $\sim$130 beta decays/hr. In $\sim$800 live hours, no events leaked into the WIMP signal region in the recoil energy range 8--115 keVr, providing an upper limit to the surface event leakage fraction of $1.7 \times 10^{-5}$ at 90% C.L. This rejection factor demonstrates that surface electrons would produce $< 0.6$ event background in the 0.3 ton-year exposure for the proposed 200-kg iZIP array in SuperCDMS SNOLAB.</blockquote>View original: <a href="http://arxiv.org/abs/1305.2405">http://arxiv.org/abs/1305.2405</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-74329101415208335402013-08-06T00:05:00.005-07:002013-08-06T00:05:02.642-07:001308.0593 (Christopher Wegg et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0593">Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red
Clump Stars</a> [<a href="http://arxiv.org/pdf/1308.0593">PDF</a>]</h2>Christopher Wegg, Ortwin Gerhard<a name='more'></a><blockquote class="abstract">The inner Milky Way is dominated by a boxy, triaxial bulge which is believed to have formed through disk instability processes. Despite its proximity, its large-scale properties are still not very well known, due to our position in the obscuring Galactic disk. Here we make a measurement of the three-dimensional density distribution of the Galactic bulge using red clump giants identified in DR1 of the VVV survey. Our density map covers the inner (2.2x1.4x1.1)kpc of the bulge/bar. Line-of-sight density distributions are estimated by deconvolving extinction and completeness corrected K-band magnitude distributions. In constructing our measurement, we assume that the three-dimensional bulge is 8-fold mirror triaxially symmetric. In doing so we measure the angle of the bar-bulge to the line-of-sight to be (27+- 2)deg, where the dominant error is systematic arising from the details of the deconvolution process. The resulting density distribution shows a highly elongated bar with projected axis ratios ~(1:2.1) for isophotes reaching ~2kpc along the major axis. Along the bar axes the density falls off roughly exponentially, with axis ratios (10:6.3:2.6) and exponential scale-lengths (0.70:0.44:0.18)kpc. From about 400pc above the Galactic plane, the bulge density distribution displays a prominent X-structure. Overall, the density distribution of the Galactic bulge is characteristic for a strongly boxy/peanut shaped bulge within a barred galaxy.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0593">http://arxiv.org/abs/1308.0593</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-83273750648316706102013-08-06T00:05:00.003-07:002013-08-06T00:05:01.593-07:001308.0597 (Matthew Nichols et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0597">The Epoch of Assembly of Two Galaxy Groups: A comparative study</a> [<a href="http://arxiv.org/pdf/1308.0597">PDF</a>]</h2>Matthew Nichols, Joss Bland-Hawthorn<a name='more'></a><blockquote class="abstract">Nearby galaxy groups of comparable mass to the Local Group show global variations that reflect differences in their evolutionary history. Satellite galaxies in groups have higher levels of gas deficiency as the distance to their host decreases. The well established gas deficiency profile of the Local Group reflects an epoch of assembly starting at z<10. We investigate whether this gas deficiency profile can be used to determine the epoch of assembly for other nearby groups. We choose the M81 group as this has the most complete inventory, both in terms of membership and multi-wavelength observations. We expand our earlier evolutionary model of satellite dwarf galaxies to not only confirm this result for the Local Group but show that the more gas-rich M81 group is likely to have assembled at a later time (z<1-3).</blockquote>View original: <a href="http://arxiv.org/abs/1308.0597">http://arxiv.org/abs/1308.0597</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-69193547549591185092013-08-06T00:05:00.001-07:002013-08-06T00:05:00.530-07:001308.0627 (Douglas A. Barros et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0627">A Galactic Ring of Minimum Stellar Density Near the Solar Orbit Radius</a> [<a href="http://arxiv.org/pdf/1308.0627">PDF</a>]</h2>Douglas A. Barros, Jacques R. D. Lépine, Thiago C. Junqueira<a name='more'></a><blockquote class="abstract">We analyse the secular effects of a long-lived Galactic spiral structure on the stellar orbits with mean radii close to the corotation resonance. By test-particle simulations and different spiral potential models with parameters constrained on observations, we verified the formation of a minimum with amplitude ~ 30% - 40% of the background disk stellar density at corotation. Such minimum is formed by the secular angular momentum transfer between stars and the spiral density wave on both sides of corotation. We demonstrate that the secular loss (gain) of angular momentum and decrease (increase) of mean orbital radius of stars just inside (outside) corotation can counterbalance the opposite trend of exchange of angular momentum shown by stars orbiting the librational points L_4/5 at the corotation circle. Such secular processes actually allow steady spiral waves to promote radial migration across corotation. We propose some observational evidences for the minimum stellar density in the Galactic disk, such as its direct relation to the minimum in the observed rotation curve of the Galaxy at the radius R ~ 9 kpc (for R_0 = 7.5 kpc), as well as its association with a minimum in the distribution of Galactic radii of a sample of open clusters older than 1 Gyr. The closeness of the solar orbit radius to the corotation resonance implies that the solar orbit lies inside a ring of minimum surface density (stellar + gas). This also implies in a correction to larger values for the estimated total mass of the Galactic disk, and consequently, a greater contribution of the disk component to the inner rotation curve of the Galaxy.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0627">http://arxiv.org/abs/1308.0627</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-15688709804999137742013-08-06T00:04:00.007-07:002013-08-06T00:04:59.484-07:001308.0646 (Brian Punsly et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0646">Calibrated Estimates of the Energy in Major Flares of GRS 1915+105</a> [<a href="http://arxiv.org/pdf/1308.0646">PDF</a>]</h2>Brian Punsly, Jerome Rodriguez<a name='more'></a><blockquote class="abstract">We analyze the energetics of the major radio flare of October 8 2005 in GRS 1915+105. The flare is of particular interest because it is one of the most luminous and energetic radio flares from a Galactic black hole that has ever been observed. The motivation is two-fold. One, to learn more about the energetics of this most extreme phenomenon and its relationship to the accretion state. The second is to verify if the calibrated estimates of the energy of major radio flares (based on the peak low frequency optically thin flux) derived from flares in the period 1996-2001 in Punsly & Rodriguez (2013), PR13 hereafter, can be used to estimate plasmoid energy beyond this time period. We find evidence that the calibrated curves are still accurate for this strong flare. Furthermore, the physically important findings of PR13 are supported by the inclusion of this flare: the flare energy is correlated with both the intrinsic bolometric X-ray luminosity, $L_{\mathrm{bol}}$, $\sim 1$ hour before ejection and $L_{\mathrm{bol}}$ averaged over the duration of the ejection of the plasmoid and $L_{\mathrm{bol}}$ is highly elevated relative to historic levels just before and during the ejection episode. A search of the data archives reveal that only the October 8 2005 flare and those in PR13 have adequate data sampling to allow estimates of both the energy of the flare and the X-ray luminosity before and during flare launch.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0646">http://arxiv.org/abs/1308.0646</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-24012679759006672042013-08-06T00:04:00.005-07:002013-08-06T00:04:56.182-07:001308.0857 (Branimir Sesar et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0857">Tracing the Orphan Stream to 55 kpc with RR Lyrae Stars</a> [<a href="http://arxiv.org/pdf/1308.0857">PDF</a>]</h2>Branimir Sesar, Carl J. Grillmair, Judith G. Cohen, Eric C. Bellm, Varun B. Bhalerao, David Levitan, Russ R. Laher, Eran O. Ofek, Jason A. Surace, Sumin Tang, Adam Waszczak, Shrinivas R. Kulkarni, Thomas A. Prince<a name='more'></a><blockquote class="abstract">We report positions, velocities and metallicities of 50 ab-type RR Lyrae (RRab) stars observed in the vicinity of the Orphan stellar stream. Using about 30 RRab stars classified as being likely members of the Orphan stream, we study the metallicity and the spatial extent of the stream. We find that RRab stars in the Orphan stream have a wide range of metallicities, from -1.5 dex to -2.7 dex. The average metallicity of the stream is -2.1 dex, identical to the value obtained by Newberg et al. (2010) using blue horizontal branch stars. We find that the most distant parts of the stream (40-50 kpc from the Sun) are about 0.3 dex more metal-poor than the closer parts (within ~30 kpc), suggesting a possible metallicity gradient along the stream's length. We have extended the previous studies and have mapped the stream up to 55 kpc from the Sun. Even after a careful search, we did not identify any more distant RRab stars that could plausibly be members of the Orphan stream. If confirmed with other tracers, this result would indicate a detection of the end of the leading arm of the stream. We have compared the distances of Orphan stream RRab stars with the best-fit orbits obtained by Newberg et al. (2010). We find that model 6 of Newberg et al. (2010) cannot explain the distances of the most remote Orphan stream RRab stars, and conclude that the best fit to distances of Orphan stream RRab stars and to the local circular velocity is provided by potentials where the total mass of the Galaxy within 60 kpc is M_{60}~2.7x10^{11} Msun, or about 60% of the mass found by previous studies. More extensive modelling that would consider non-spherical potentials and the possibility of misalignment between the stream and the orbit, is highly encouraged.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0857">http://arxiv.org/abs/1308.0857</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-22201211973171747432013-08-06T00:04:00.003-07:002013-08-06T00:04:55.092-07:001308.0956 (Rainer M. Buchholz et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0956">Ks- and Lp-band polarimetry on stellar and bow-shock sources in the
Galactic center</a> [<a href="http://arxiv.org/pdf/1308.0956">PDF</a>]</h2>Rainer M. Buchholz, Gunther Witzel, Rainer Schoedel, Andreas Eckart<a name='more'></a><blockquote class="abstract">Infrared observations of the Galactic center (GC) provide a unique opportunity to study stellar and bow-shock polarization effects in a dusty environment. The goals of this work are to present new Ks- and Lp-band polarimetry on an unprecedented number of sources in the central parsec of the GC, thereby expanding our previous results in the H- and Ks-bands. We use AO-assisted Ks- and Lp-band observations, obtained at the ESO VLT. High precision photometry and the new polarimetric calibration method for NACO allow us to map the polarization in a region of 8" x 25" (Ks) resp. 26" x 28" (Lp). These are the first polarimetric observations of the GC in the Lp-band in 30 years, with vastly improved spatial resolution compared to previous results. This allows resolved polarimetry on bright bow-shock sources in this area for the first time at this wavelength. We find foreground polarization to be largely parallel to the Galactic plane (Ks-band: 6.1% at 20 degrees, Lp-band: 4.5% at 20 degrees, in good agreement with our previous findings and with older results. The previously described Lp-band excess in the foregound polarization towards the GC could be confirmed here for a much larger number of sources. The bow-shock sources contained in the FOV seem to show a different relation between the polarization in the observed wavelength bands than what was determined for the foreground. This points to the different relevant polarization mechanisms. The resolved polarization patterns of IRS 5 and 10W match the findings we presented earlier for IRS~1W. Additionally, intrinsic Lp-band polarization was measured for IRS 1W and 21, as well as for other, less prominent MIR-excess sources (IRS 2S, 2L, 5NE). The new data offer support for the presumed bow-shock nature of several of these sources (1W, 5, 5NE, 10W, 21) and for the model of bow-shock polarization presented in our last work.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0956">http://arxiv.org/abs/1308.0956</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-58457280491662085252013-08-06T00:04:00.001-07:002013-08-06T00:04:54.110-07:001308.1036 (Yoshito Shimajiri et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.1036">Extensive [CI] Mapping toward the Orion-A Molecular Cloud</a> [<a href="http://arxiv.org/pdf/1308.1036">PDF</a>]</h2>Yoshito Shimajiri, Takeshi Sakai, Takashi Tsukagoshi, Yoshimi Kitamura, Munetake Momose, Masao Saito, Tai Oshima, Kotaro Kohno, Ryohei Kawabe<a name='more'></a><blockquote class="abstract">We have carried out wide-field (0.17 degree^2) and high-angular resolution (21.3 arcsec ~ 0.04 pc) observations in [CI] line toward the Orion-A giant molecular cloud with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in the On-The-Fly (OTF) mode. Overall features of the [CI] emission are similar to those of the CO (1--0) emission in Shimajiri et al. 2011; the total intensity ratio of the [CI] to CO emission ranges from 0.05 to 0.2. The optical depth of the [CI] emission is found to be 0.1 -- 0.75, suggesting optically thin emission. The column density of the [CI] emission is estimated to be (1.0 -- 19) x 10^17 cm^-2. These results are consistent with the results of the previous [CI] observations with a low-angular resolution of 2.2 arcmin (e.g. Ikeda et al. 1999). In the nearly edge-on PDRs and their candidates of the Orion Bar, DLSF, M 43 Shell, and Region D, the distributions of the [CI] emission coincide with those of the CO emission, inconsistent with the prediction by the plane-parallel PDR model (Hollenbach & Tielens 1999). In addition, the [CI] distribution in the Orion A cloud is found to be more similar to those of the ^{13}CO (1--0), C^{18}O (1--0), and H^{13}CO^+ (1--0) lines than that of the CO (1--0) line, suggesting that the [CI] emission is not limited to the cloud surface, but is tracing the dense, inner parts of the cloud.</blockquote>View original: <a href="http://arxiv.org/abs/1308.1036">http://arxiv.org/abs/1308.1036</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-22684769432483578922013-08-05T00:03:00.011-07:002013-08-05T00:03:57.110-07:001308.0339 (Samantha M. Benincasa et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0339">Giant Molecular Cloud Formation in Disk Galaxies: Characterizing
Simulated versus Observed Cloud Catalogues</a> [<a href="http://arxiv.org/pdf/1308.0339">PDF</a>]</h2>Samantha M. Benincasa, Elizabeth J. Tasker, Ralph E. Pudritz, James Wadsley<a name='more'></a><blockquote class="abstract">We present the results of a study of simulated Giant Molecular Clouds (GMCs) formed in a Milky Way-type galactic disk with a flat rotation curve. This simulation, which does not include star formation or feedback, produces clouds with masses ranging between 10^4 Msun and 10^7 Msun. We compare our simulated cloud population to two observational surveys; The Boston University- Five College Radio Astronomy Observatory Galactic Ring Survey and the BIMA All-Disk Survey of M33. An analysis of the global cloud properties as well as a comparison of Larson's scaling relations is carried out. We find that simulated cloud properties agree well with the observed cloud properties, with the closest agreement occurring between the clouds at comparable resolution in M33. Our clouds are highly filamentary - a property that derives both from their formation due to gravitational instability in the sheared galactic environment, as well as to cloud- cloud gravitational encounters. We also find that the rate at which potentially star forming gas accumulates within dense regions - wherein n_{thresh} > 10^4 cm^{-3} - is 3% per 10 Myr, in clouds of roughly 10^6 Msun. This suggests that star formation rates in observed clouds are related to the rates at which gas can be accumulated into dense subregions within GMCs via filamentary flows. The most internally well-resolved clouds are chosen for listing in a catalogue of simulated GMCs; the first of its kind. The catalogued clouds are available as an extracted data set from the global simulation.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0339">http://arxiv.org/abs/1308.0339</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-33365759044396323332013-08-05T00:03:00.009-07:002013-08-05T00:03:56.365-07:001308.0351 (G. Zasowski et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0351">Target Selection for the Apache Point Observatory Galactic Evolution
Experiment (APOGEE)</a> [<a href="http://arxiv.org/pdf/1308.0351">PDF</a>]</h2>G. Zasowski, Jennifer A. Johnson, P. M. Frinchaboy, S. R. Majewski, D. L. Nidever, H. J. Rocha Pinto, L. Girardi, B. Andrews, S. D. Chojnowski, K. M. Cudworth, K. Jackson, J. Munn, M. F. Skrutskie, R. L. Beaton, C. H. Blake, K. Covey, R. Deshpande, C. Epstein, D. Fabbian, S. W. Fleming, A. Garcia Hernandez, A. Herrero, S. Mahadevan, Sz. Meszaros, M. Schultheis, K. Sellgren, R. Terrien, J. van Saders, C. Allende Prieto, D. Bizyaev, A. Burton, K. Cunha, L. N. da Costa, S. Hasselquist, F. Hearty, J. Holtzman, A. E. Garcia Perez, M. A. G. Maia, R. W. O'Connell, C. O'Donnell, M. Pinsonneault, B. X. Santiago, R. P. Schiavon, M. Shetrone, V. Smith, J. C. Wilson<a name='more'></a><blockquote class="abstract">The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution infrared spectroscopic survey spanning all Galactic environments (i.e., bulge, disk, and halo), with the principal goal of constraining dynamical and chemical evolution models of the Milky Way. APOGEE takes advantage of the reduced effects of extinction at infrared wavelengths to observe the inner Galaxy and bulge at an unprecedented level of detail. The survey's broad spatial and wavelength coverage enables users of APOGEE data to address numerous Galactic structure and stellar populations issues. In this paper we describe the APOGEE targeting scheme and document its various target classes to provide the necessary background and reference information to analyze samples of APOGEE data with awareness of the imposed selection criteria and resulting sample properties. APOGEE's primary sample consists of ~100,000 red giant stars, selected to minimize observational biases in age and metallicity. We present the methodology and considerations that drive the selection of this sample and evaluate the accuracy, efficiency, and caveats of the selection and sampling algorithms. We also describe additional target classes that contribute to the APOGEE sample, including numerous ancillary science programs, and we outline the targeting data that will be included in the public data releases.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0351">http://arxiv.org/abs/1308.0351</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-14084437188322803322013-08-05T00:03:00.007-07:002013-08-05T00:03:55.345-07:001308.0357 (Lovro Palaversa et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0357">Exploring the Variable Sky with LINEAR. III. Classification of Periodic
Light Curves</a> [<a href="http://arxiv.org/pdf/1308.0357">PDF</a>]</h2>Lovro Palaversa, Željko Ivezić, Laurent Eyer, Domagoj Ruždjak, Davor Sudar, Mario Galin, Andrea Kroflin, Martina Mesarić, Petra Munk, Dijana Vrbanec, Hrvoje Božić, Sarah Loebman, Branimir Sesar, Lorenzo Rimoldini, Nicholas Hunt-Walker, Jacob VanderPlas, David Westman, J. Scott Stuart, Andrew C. Becker, Gregor Srdoč, Przemyslaw Wozniak, Hakeem Oluseyi<a name='more'></a><blockquote class="abstract">We describe the construction of a highly reliable sample of approximately 7,000 optically faint periodic variable stars with light curves obtained by the asteroid survey LINEAR across 10,000 sq.deg of northern sky. Majority of these variables have not been cataloged yet. The sample flux limit is several magnitudes fainter than for most other wide-angle surveys; the photometric errors range from ~0.03 mag at $r=15$ to ~0.20 mag at r=18. Light curves include on average 250 data points, collected over about a decade. Using SDSS-based photometric recalibration of the LINEAR data for about 25 million objects, we selected ~200,000 most probable candidate variables and visually confirmed and classified approximately 7,000 periodic variables using phased light curves. The reliability and uniformity of visual classification across eight human classifiers was calibrated and tested using a SDSS Stripe 82 region variable star catalog, and verified using an unsupervised machine learning approach. The resulting sample of periodic LINEAR variables is dominated by 3,900 RR Lyrae stars and 2,700 eclipsing binary stars of all subtypes, and includes small fractions of relatively rare populations such as asymptotic giant branch stars and SX Phoenicis stars. We discuss the distribution of these mostly uncataloged variables in various diagrams constructed with optical-to-infrared SDSS, 2MASS and WISE photometry, and with LINEAR light curve features. An interesting side result is a robust and precise quantitative description of a strong correlation between the light-curve period and color/spectral type for close and contact eclipsing binary stars. These large samples of robustly classified variable stars will enable detailed statistical studies of the Galactic structure and physics of binary and other stars, and we make them publicly available.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0357">http://arxiv.org/abs/1308.0357</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-86830357157127280242013-08-05T00:03:00.005-07:002013-08-05T00:03:54.537-07:001308.0432 (Luke Chamandy et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0432">Magnetic arms generated by multiple interfering galactic spiral patterns</a> [<a href="http://arxiv.org/pdf/1308.0432">PDF</a>]</h2>Luke Chamandy, Kandaswamy Subramanian, Alice Quillen<a name='more'></a><blockquote class="abstract">Interfering two- and three-arm spiral patterns have previously been inferred to exist in many galaxies and also in numerical simulations, and invoked to explain important dynamical properties, such as lack of symmetry, kinks in spiral arms, and star formation in armlets. The non-axisymmetric galactic mean-field dynamo model of Chamandy et al. 2013a is generalized to allow for such multiple co-existing spiral patterns in the kinetic alpha effect, leading to the existence of magnetic spiral arms in the large-scale magnetic field with several new properties. The large-scale magnetic field produced by an evolving superposition of two- and three-arm patterns evolves with time along with the superposition. Magnetic arms can be stronger and more extended in radius and in azimuth when produced by two interfering patterns rather than by one pattern acting alone. Transient morphological features arise in the magnetic arms, including bifurcations, disconnected armlets, and temporal and spatial variation in arm strength and winding angle. The magnetic field is sometimes strongest in between the \alpha_k-arms, unlike in standard models with a single pattern, where it is strongest within the \alpha_k-arms. Moreover, some amount of m=1 azimuthal symmetry is found to be present in the magnetic field, which is generally not the case for forcing by single two- or three-arm patterns. Many of these results are reminiscent of observed features in the regular magnetic fields of nearby spiral galaxies, like NGC 6946 and IC 342, which have previously been inferred to have significant two- and three-arm spiral patterns.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0432">http://arxiv.org/abs/1308.0432</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-84200063214053352992013-08-05T00:03:00.003-07:002013-08-05T00:03:53.766-07:001308.0495 (D. J. Pinfield et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0495">A deep WISE search for very late type objects and the discovery of two
halo/thick-disk T dwarfs: WISE 0013+0634 and WISE 0833+0052</a> [<a href="http://arxiv.org/pdf/1308.0495">PDF</a>]</h2>D. J. Pinfield, J. Gomes, A. C. Day-Jones, S. K. Leggett, M. Gromadzki, B. Burningham, M. T. Ruiz, R. Kurtev, T. Cattermole, C. Cardoso, N. Lodieu, J. Faherty, S. Littlefair, R. Smart, M. Irwin, J. R. A. Clarke, L. Smith, P. W. Lucas, M. C. Galvez-Ortiz, J. S. Jenkins, H. R. A. Jones, R. Rebolo, V. J. S. Bejar, B. Gauza<a name='more'></a><blockquote class="abstract">A method is defined for identifying late T and Y dwarfs in WISE down to low values of signal-to-noise. This requires a WISE detection only in the W2-band and uses the statistical properties of the WISE multi-frame measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources. To trace our desired parameter space we use a control sample of isolated non-moving non-variable point sources from the SDSS, and identify a sample of 158 WISE W2-only candidates down to a signal-to-noise limit of 8. For signal-to-noise ranges >10 and 8-10 respectively, ~45% and ~90% of our sample fall outside the selection criteria published by the WISE team (Kirkpatrick et al. 2012), due mainly to the type of constraints placed on the number of individual W2 detections. We present follow-up of eight candidates and identify WISE 0013+0634 and WISE 0833+0052, T8 and T9 dwarfs with high proper motion (~1.3 and ~1.8 arcsec/yr). Both objects show a mid-infrared/near-infrared excess of ~1-1.5 magnitudes, and are K-band suppressed. Distance estimates lead to space motion constraints that suggest halo (or at least thick disk) kinematics. We then assess the reduced proper motion diagram of WISE ultracool dwarfs, which suggests that late T and Y dwarfs may have a higher thick-disk/halo population fraction than earlier objects.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0495">http://arxiv.org/abs/1308.0495</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-64594529509770183952013-08-05T00:03:00.001-07:002013-08-05T00:03:52.638-07:001308.0501 (J. Frith et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0501">A catalogue of bright (K < 9) M dwarfs</a> [<a href="http://arxiv.org/pdf/1308.0501">PDF</a>]</h2>J. Frith, D. J. Pinfield, H. R. A. Jones, J. R. Barnes, Y. Pavlenko, E. L. Martin, C. Brown, M. K. Kuznetsov, F. Marocco, R. Tata, M. Cappetta<a name='more'></a><blockquote class="abstract">Using the Position and Proper Motion Extended-L (PPMXL) catalogue, we have used optical and near-infrared colour cuts together with a reduced proper motion cut to find bright M dwarfs for future exoplanet transit studies. PPMXL's low proper motion uncertainties allow us to probe down to smaller proper motions than previous similar studies. We have combined unique objects found with this method to that of previous work to produce 8479 K<9 M dwarfs. Low resolution spectroscopy was obtained of a sample of the objects found using this selection method to gain statistics on their spectral type and physical properties. Results show a spectral type range of K7-M4V. This catalogue is the most complete collection of K<9 M dwarfs currently available and is made available here.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0501">http://arxiv.org/abs/1308.0501</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-44087622981464021352013-08-04T00:06:00.009-07:002013-08-04T00:06:08.007-07:001308.0032 (B. M. S. Hansen et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0032">An Age Difference of 2 Gyr between a Metal-Rich and a Metal-Poor
Globular Cluster</a> [<a href="http://arxiv.org/pdf/1308.0032">PDF</a>]</h2>B. M. S. Hansen, J. S. Kalirai, J. Anderson, A. Dotter, H. B. Richer, R. M. Rich, M. M. Shara, G. G. Fahlman, J. R. Hurley, I. R. King, D. Reitzel, P. B. Stetson<a name='more'></a><blockquote class="abstract">Globular clusters trace the formation history of the spheroidal components of both our Galaxy and others, which represent the bulk of star formation over the history of the universe. They also exhibit a range of metallicities, with metal-poor clusters dominating the stellar halo of the Galaxy, and higher metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and later swallowed along with their original host galaxies, and which were formed in situ. Here we present an age determination of the metal-rich globular cluster 47 Tucanae by fitting the properties of the cluster white dwarf population, which implies an absolute age of 9.9 (0.7) Gyr at 95% confidence. This is about 2.0 Gyr younger than inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than the metal-poor halo clusters like NGC 6397.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0032">http://arxiv.org/abs/1308.0032</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-67146380334764925702013-08-04T00:06:00.007-07:002013-08-04T00:06:07.402-07:001308.0054 (Daniel H. McIntosh et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0054">Massive blue early-type galaxies in the SDSS. I. A new population of
recently quenched elliptical galaxies</a> [<a href="http://arxiv.org/pdf/1308.0054">PDF</a>]</h2>Daniel H. McIntosh, Cory Wagner, Andrew Cooper, Eric F. Bell, Dusan Keres, Frank C. van den Bosch, Anna Gallazzi, Tim Haines, Justin Mann, Anna Pasquali, Allison M. Christian<a name='more'></a><blockquote class="abstract">We use the SDSS to explore early-type galaxies (ETGs) that are plausibly in transition between the red sequence and the blue cloud. Through careful morphological inspection, we identify 1500 unusually blue elliptical galaxies among a larger sample of blue ETGs with 0.01<z<0.08 and M_star>1e10 h^{-2} M_sun. Blue ellipticals comprise 3.7% of all ETGs with 1e10<M_star<1e11 h^{-2} M_sun. Using fiber spectra diagnostics, we find a unique population of 172 non-star-forming ellipticals with distinctly blue urz colors and <3Gyr stellar ages. These recently quenched ellipticals (RQEs) have n=2.7-4.7x10^{-5}h^3 Mpc^{-3} and sufficient numbers above 2.5e10 h^{-2} M_sun to account for >50% of the expected quiescent growth at z~0 assuming this phase lasts 0.5Gyr. Based on color, stellar M/L ratios and metallicity estimates, we argue that RQEs have recent SFHs that differ from rejuvenated ETGs. Yet, a significant but small incidence (5%) of RQEs with E+A spectra implies that the quenching of most RQEs did not involve a large starburst. Most (90%) RQEs reside at the centers of 3x10^{12}h^{-1} M_sun groups, which agrees well with the `small group scale' in which spiral merging onto the halo center is maximally efficient. The preferred RQE environment rules out satellite-specific quenching processes for most. Under the assumption that most RQEs were quenched by a hot halo atmosphere impeding efficient gas cooling, we discuss the incidence of Seyfert and LINER activity with regards to the maintenance-mode feedback needed to keep star formation shut off at the centers of such small halos. (abridged)</blockquote>View original: <a href="http://arxiv.org/abs/1308.0054">http://arxiv.org/abs/1308.0054</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-27492557692514516072013-08-04T00:06:00.005-07:002013-08-04T00:06:06.408-07:001308.0108 (Valery V. Kiselev)<h2 class="title"><a href="http://arxiv.org/abs/1308.0108">Genesis of spiral galaxies</a> [<a href="http://arxiv.org/pdf/1308.0108">PDF</a>]</h2>Valery V. Kiselev<a name='more'></a><blockquote class="abstract">Enigmatic spiral structure of many galaxies and its huge orbital momentum originated due to the capture of lightweight bare black hole by gravity of heavy primordial gas cloud at large impact parameter. The rotating of black hole caused the formation of accretion disc from the cloud and the transfer of orbital momentum to the disc, while during the fall to the center of mass, the spiral trace of black hole in the disc did create the spiral front line of sound waves in the gas, that further evolved into the stellar spiral arms. This mechanism opens the way to study features of spiral galaxy formation, say, an influence and a significance of dark matter in this process.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0108">http://arxiv.org/abs/1308.0108</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-59537794164555790062013-08-04T00:06:00.003-07:002013-08-04T00:06:05.655-07:001308.0134 (S. L. Lumsden et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0134">The Red MSX Source Survey: the Massive Young Stellar Population of our
Galaxy</a> [<a href="http://arxiv.org/pdf/1308.0134">PDF</a>]</h2>S. L. Lumsden, M. G. Hoare, J. S. Urquhart, R. D. Oudmaijer, B. Davies, J. C. Mottram, H. D. B. Cooper, T. J. T. Moore<a name='more'></a><blockquote class="abstract">We present the Red MSX Source (RMS) Survey, the largest statistically selected catalog of young massive protostars and HII regions to date. We outline the construction of the catalog using mid and near infrared color selection, as well as the detailed follow up work at other wavelengths, and at higher spatial resolution in the infrared. We show that within the adopted selection bounds we are more than 90% complete for the massive protostellar population, with a positional accuracy of the exciting source of better than 2 arcseconds. We briefly summarize some of the results that can be obtained from studying the properties of the objects in the catalog as a whole, and find evidence that the most massive stars form: (i) preferentially nearer the Galactic centre than the anti-centre; (ii) in the most heavily reddened environments, suggestive of high accretion rates; and (iii) from the most massive cloud cores.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0134">http://arxiv.org/abs/1308.0134</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-87111849998019493072013-08-04T00:06:00.001-07:002013-08-04T00:06:04.770-07:001308.0261 (Orlin Stanchev et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0261">Relationship between molecular cloud structure and density PDFs</a> [<a href="http://arxiv.org/pdf/1308.0261">PDF</a>]</h2>Orlin Stanchev, Sava Donkov, Todor V. Veltchev, Rahul Shetty<a name='more'></a><blockquote class="abstract">Volume and column density PDFs in molecular clouds are important diagnostics for understanding their general structure. We developed a novel approach to trace the cloud structure by varying the lower PDF cut-off and exploring a suggested mass-density relationship with a power-law index $x^\prime$. The correspondence of x' as a function of spatial scale to the slope of the high-density PDF tail is studied. To validate the proposed model, we use results from hydrodynamical simulations of a turbulent self-gravitating cloud and recent data on dust continuum emission from the Planck mission.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0261">http://arxiv.org/abs/1308.0261</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-67398908054190218402013-08-01T00:34:00.021-07:002013-08-01T00:34:24.803-07:001307.8118 (C. F. Manara et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8118">Accurate determination of accretion and photospheric parameters in Young
Stellar Objects: the case of two candidate old disks in the Orion Nebula
Cluster</a> [<a href="http://arxiv.org/pdf/1307.8118">PDF</a>]</h2>C. F. Manara, G. Beccari, N. Da Rio, G. De Marchi, A. Natta, L. Ricci, M. Robberto, L. Testi<a name='more'></a><blockquote class="abstract">Current planet formation models are largely based on the observational constraint that protoplanetary disks have lifetime 3Myr. Recent studies, however, report the existence of PMS stars with signatures of accretion (strictly connected with the presence of circumstellar disks)and photometrically determined ages of 30 Myr, or more. Here we present a spectroscopic study of two major age outliers in the ONC. We use broad band, intermediate resolution VLT/X-Shooter spectra combined with an accurate method to determine the stellar parameters and the related age of the targets to confirm their peculiar age estimates and the presence of ongoing accretion.The analysis is based on a multi-component fitting technique, which derives simultaneously SpT, extinction, and accretion properties of the objects. With this method we confirm and quantify the ongoing accretion. From the photospheric parameters of the stars we derive their position on the HRD, and the age given by evolutionary models. Together with other age indicators like the lithium equivalent width we estimate with high accuracy the age of the objects. Our study shows that the two objects analyzed are not older than the typical population of the ONC. Our results show that, while photometric determination of the photospheric parameters are an accurate method to estimate the parameters of the bulk of young stellar populations, those of individual objects with high accretion rates and extinction may be affected by large uncertainties. Broad band spectroscopic determinations should thus be used to confirm the nature of individual objects. Our analysis shows that this method allows us to obtain an accurate determination of the photospheric parameters of accreting YSOs in any nearby star-forming region. We suggest that our detailed, broad- band spectroscopy method should be used to derive accurate properties of candidate old and accreting YSOs.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8118">http://arxiv.org/abs/1307.8118</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-42684490964809710872013-08-01T00:34:00.019-07:002013-08-01T00:34:24.031-07:001307.8116 (Eugene Vasiliev)<h2 class="title"><a href="http://arxiv.org/abs/1307.8116">A new code for orbit analysis and Schwarzschild modelling of triaxial
stellar systems</a> [<a href="http://arxiv.org/pdf/1307.8116">PDF</a>]</h2>Eugene Vasiliev<a name='more'></a><blockquote class="abstract">We review the methods used to study the orbital structure and chaotic properties of various galactic models and to construct self-consistent equilibrium solutions by Schwarzschild's orbit superposition technique. These methods are implemented in a new publicly available software tool, SMILE, which is intended to be a convenient and interactive instrument for studying a variety of 2D and 3D models, including arbitrary potentials represented by a basis-set expansion, a spherical-harmonic expansion with coefficients being smooth functions of radius (splines), or a set of fixed point masses. We also propose two new variants of Schwarzschild modelling, in which the density of each orbit is represented by the coefficients of the basis-set or spline spherical-harmonic expansion, and the orbit weights are assigned in such a way as to reproduce the coefficients of the underlying density model. We explore the accuracy of these general-purpose potential expansions and show that they may be efficiently used to approximate a wide range of analytic density models and serve as smooth representations of discrete particle sets (e.g. snapshots from an N-body simulation), for instance, for the purpose of orbit analysis of the snapshot. For the variants of Schwarzschild modelling, we use two test cases - a triaxial Dehnen model containing a central black hole, and a model re-created from an N-body snapshot obtained by a cold collapse. These tests demonstrate that all modelling approaches are capable of creating equilibrium models.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8116">http://arxiv.org/abs/1307.8116</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-23047519209133407902013-08-01T00:34:00.017-07:002013-08-01T00:34:21.710-07:001307.8124 (B. Goldman et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8124">Towards a complete stellar mass function of the Hyades. I. Pan-STARRS1
optical observations of the low-mass stellar content</a> [<a href="http://arxiv.org/pdf/1307.8124">PDF</a>]</h2>B. Goldman, S. Röser, E. Schilbach, E. A. Magnier, C. Olczak, T. Henning, M. Juric, E. Schlafly, W. P. Chen, I. Platais, W. Burgett, K. Hodapp, J. Heasley, R. P. Kudritzki, J. S. Morgan, P. A. Price, J. L. Tonry, R. Wainscoat, the PS1 Science Consortium<a name='more'></a><blockquote class="abstract">The Hyades cluster is an ideal target to study the dynamical evolution of a star cluster over the entire mass range due to its intermediate age and proximity to the Sun. We wanted to extend the Hyades mass function towards lower masses down to 0.1 Msol and to use the full three-dimensional spatial information to characterize the dynamical evolution of the cluster. We performed a kinematic and photometric selection using the PPMXL and Pan-STARRS1 sky surveys, to search for cluster members up to 30 pc from the cluster centre. We determined our detection efficiency and field star contamination rate to derive the cluster luminosity and mass functions down to masses of 0.1 Msol. The thorough astrometric and photometric constraints minimized the contamination. A minimum spanning tree algorithm was used to quantify the mass segregation. We discovered 43 new Hyades member candidates with velocity perpendicular to the Hyades motion up to 2 km/s. They have mass estimates between 0.43 and 0.09 Msol, for a total mass of 10 Msol. This doubles the number of Hyades candidates with masses smaller than 0.15 Msol. We provide an additional list of 11 possible candidates with velocity perpendicular to the Hyades motion up to 4 km/s. The cluster is significantly mass segregated. The extension of the mass function towards lower masses provided an even clearer signature than estimated in the past. We also identified as likely Hyades member an L0 dwarf previously assumed to be a field dwarf. Finally we question the membership of a number of previously published candidates, including a L2.5-type dwarf.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8124">http://arxiv.org/abs/1307.8124</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-73993170240289124312013-08-01T00:34:00.015-07:002013-08-01T00:34:20.767-07:001307.8215 (Yoshiaki Sofue)<h2 class="title"><a href="http://arxiv.org/abs/1307.8215">The Mass Distribution and Rotation Curve in the Galaxy</a> [<a href="http://arxiv.org/pdf/1307.8215">PDF</a>]</h2>Yoshiaki Sofue<a name='more'></a><blockquote class="abstract">The mass distribution in the Galaxy is determined by dynamical and photometric methods. Rotation curves are the major tool for determining the dynamical mass distribution in the Milky Way and spiral galaxies. The photometric (statistical) method utilizes luminosity profiles from optical and infrared observations, and assumes empirical values of the mass-to-luminosity (M/L) ratio to convert the luminosity to mass. In this chapter the dynamical method is described in detail, and rotation curves and mass distribution in the Milky Way and nearby spiral galaxies are presented. The dynamical method is categorized into two methods: the decomposition method and direct method. The former fits the rotation curve by calculated curve assuming several mass components such as a bulge, disk and halo, and adjust the dynamical parameters of each component. Explanations are given of the mass profiles as the de Vaucouleurs law, exponential disk, and dark halo profiles inferred from numerical simulations. Another method is the direct method, with which the mass distribution can be directly calculated from the data of rotation velocities without employing any mass models. Some results from both methods are presented, and the Galactic structure is discussed in terms of the mass. Rotation curves and mass distributions in external galaxies are also discussed, and the fundamental mass structures are shown to be universal.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8215">http://arxiv.org/abs/1307.8215</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-33699611132727514132013-08-01T00:34:00.013-07:002013-08-01T00:34:19.831-07:001307.8241 (Yoshiaki Sofue)<h2 class="title"><a href="http://arxiv.org/abs/1307.8241">Rotation Curve and Mass Distribution in the Galactic Center --- From
Black Hole to Entire Galaxy ---</a> [<a href="http://arxiv.org/pdf/1307.8241">PDF</a>]</h2>Yoshiaki Sofue<a name='more'></a><blockquote class="abstract">Analyzing high-resolution longitude-velocity (LV) diagrams of the Galactic Center observed with the Nobeyama 45-m telescope in the CO and CS line emissions, we obtain a central rotation curve of the Milky Way. We combine it with the data for the outer disk, and construct a logarithmic rotation curve of the entire Galaxy. The new rotation curve covers a wide range of radius from r ~ 1 pc to several hundred kpc without a gap of data points. It links, for the first time, the kinematical characteristics of the Galaxy from the central black hole to the bulge, disk and dark halo. Using this grand rotation curve, we calculate the radial distribution of surface mass density in the entire Galaxy, where the radius and derived mass densities vary over a dynamical range with several orders of magnitudes. We show that the galactic bulge is deconvolved into two components: the inner (core) and main bulges. Both the two bulge components are represented by exponential density profiles, but the de Vaucouleurs law was found to fail in representing the mass profile of the galactic bulge.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8241">http://arxiv.org/abs/1307.8241</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-84120904980024743.post-25578610602482127382013-08-01T00:34:00.011-07:002013-08-01T00:34:18.921-07:001307.8374 (Paul F. Goldsmith)<h2 class="title"><a href="http://arxiv.org/abs/1307.8374">Diffuse Molecular Cloud Densities from UV Measurements of CO Absorption</a> [<a href="http://arxiv.org/pdf/1307.8374">PDF</a>]</h2>Paul F. Goldsmith<a name='more'></a><blockquote class="abstract">We use UV measurements of interstellar CO towards nearby stars to calculate the density in the diffuse molecular clouds containing the molecules responsible for the observed absorption. Chemical models and recent calculations of the excitation rate coefficients indicate that the regions in which CO is found have hydrogen predominantly in molecular form. We carry out statistical equilibrium calculations using CO-H2 collision rates to solve for the H2 density in the observed sources without including effects of radiative trapping. We have assumed kinetic temperatures of 50 K and 100 K, finding this choice to make relatively little difference to the lowest transition. For the sources having T_ex(1-0) only, for which we could determine upper and lower density limits, we find <n(H2)> = 49 cm-3. While we can find a consistent density range for a good fraction of the sources having either two or three values of the excitation temperature, there is a suggestion that the higher-J transitions are sampling clouds or regions within diffuse molecular cloud material that have higher densities than the material sampled by the J = 1-0 transition. The assumed kinetic temperature and derived H2 density are anticorrelated when the J = 2-1 transition data, the J = 3-2 transition data, or both are included. For sources with either two or three values of the excitation temperature, we find average values of the midpoint of the density range that is consistent with all of the observations equal to 68 cm-3 for T_k = 100 K and 92 cm-3 for T_k = 50 K. The data for this set of sources imply that diffuse molecular clouds are characterized by an average thermal pressure between 4600 and 6800 Kcm-3.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8374">http://arxiv.org/abs/1307.8374</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0