Browsing by Subject "stellar"

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The Black Hole Mass-Galaxy Luminosity Relationship For Sloan Digital Sky Survey Quasars
(2015-02) Salviander, Sarah; Shields, Gregory A.; Bonning, E. W.; Salviander, Sarah; Shields, Gregory A.
We investigate the relationship between the mass of the central supermassive black hole, M-BH, and the host galaxy luminosity, L-gal, in a sample of quasars from the Sloan Digital Sky Survey Data Release 7. We use composite quasar spectra binned by black hole mass and redshift to assess galaxy features that would otherwise be overwhelmed by noise in individual spectra. The black hole mass is calculated using the photoionization method, and the host galaxy luminosity is inferred from the depth of the Ca II H+K features in the composite spectra. We evaluate the evolution in the M-BH-L-gal relationship by examining the redshift dependence of Delta log M-BH, the offset in M-BH from the local M-BH-L-gal relationship. There is little systematic trend in. log MBH out to z = 0.8. Using the width of the [O III] emission line as a proxy for the stellar velocity dispersion, sigma(*), we find agreement of our derived host luminosities with the locally observed Faber-Jackson relation. This supports the utility of the width of the [O III] line as a proxy for sigma(*) in statistical studies.
Bulges Of Nearby Galaxies With Spitzer: Scaling Relations In Pseudobulges And Classical Bulges
(2010-06) Fisher, David B.; Drory, Niv; Fisher, David B.
We investigate scaling relations of bulges using bulge-disk decompositions at 3.6 mu m and present bulge classifications for 173 E-Sd galaxies within 20 Mpc. Pseudobulges and classical bulges are identified using Sersic index, Hubble Space Telescope morphology, and star formation activity ( traced by 8 mu m emission). In the near-IR pseudobulges have n(b) < 2 and classical bulges have n(b) > 2, as found in the optical. Sersic index and morphology are essentially equivalent properties for bulge classification purposes. We confirm, using a much more robust sample, that the Sersic index of pseudobulges is uncorrelated with other bulge structural properties, unlike for classical bulges and elliptical galaxies. Also, the half-light radius of pseudobulges is not correlated with any other bulge property. We also find a new correlation between surface brightness and pseudobulge luminosity; pseudobulges become more luminous as they become more dense. Classical bulges follow the well-known scaling relations between surface brightness, luminosity, and half-light radius that are established by elliptical galaxies. We show that those pseudobulges (as indicated by Sersic index and nuclear morphology) that have low specific star formation rates are very similar to models of galaxies in which both a pseudobulge and classical bulge exist. Therefore, pseudobulge identification that relies only on structural indicators is incomplete. Our results, especially those on scaling relations, imply that pseudobulges are very different types of objects than elliptical galaxies.
CANDELS Observations Of The Environmental Dependence Of The Color-Mass-Morphology Relation At Z=1.6
(2013-06) Bassett, Robert; Papovich, Casey; Lotz, Jennifer M.; Bell, Eric F.; Finkelstein, Steven L.; Newman, Jeffrey A.; Tran, Kim-Vy; Almaini, Omar; Lani, Caterina; Cooper, Michael; Croton, Darren; Dekel, Avishai; Ferguson, Henry C.; Kocevski, Dale D.; Koekemoer, Anton M.; Koo, David C.; McGrath, Elizabeth J.; McIntosh, Daniel H.; Wechsler, Risa; Finkelstein, Steven L.
We study the environmental dependence of color, stellar mass, and morphology by comparing galaxies in a forming cluster to those in the field at z = 1.6 with Hubble Space Telescope near-infrared imaging in the CANDELS/UDS field. We quantify the morphology of the galaxies using the effective radius, r(eff), and Sersic index, n. In both the cluster and field, approximately half of the bulge-dominated galaxies (n > 2) reside on the red sequence of the color-magnitude diagram, and most disk-dominated galaxies (n < 2) have colors expected for star-forming galaxies. There is weak evidence that cluster galaxies have redder rest-frame U - B colors and higher stellar masses compared to the field. Star-forming galaxies in both the cluster and field show no significant differences in their morphologies. In contrast, there is evidence that quiescent galaxies in the cluster have larger median effective radii and smaller Sersic indices compared to the field with a significance of 2 sigma. These differences are most pronounced for galaxies at clustercentric distances 1 Mpc < R-proj < 1.5 Mpc, which have low Sersic indices and possibly larger effective radii, more consistent with star-forming galaxies at this epoch and in contrast to other quiescent galaxies. We argue that star-forming galaxies are processed under the influence of the cluster environment at distances greater than the cluster-halo virial radius. Our results are consistent with models where gas accretion onto these galaxies is suppressed from processes associated with the cluster environment.
Chandra Grating Spectroscopy Of Three Hot White Dwarfs
(2012-10) Adamczak, J.; Werner, K.; Rauch, T.; Schuh, S.; Drake, J. J.; Kruk, J. W.; Adamczak, J.
Context. High-resolution soft X-ray spectroscopic observations of single hot white dwarfs are scarce. With the Chandra Low-Energy Transmission Grating, we have observed two white dwarfs, one is of spectral type DA (LB 1919) and the other is a non-DA of spectral type PG1159 (PG1520+525). The spectra of both stars are analyzed, together with an archival Chandra spectrum of another DA white dwarf (GD246). Aims. The soft X-ray spectra of the two DA white dwarfs are investigated in order to study the effect of gravitational settling and radiative levitation of metals in their photospheres. LB1919 is of interest because it has a significantly lower metallicity than DAs with otherwise similar atmospheric parameters. GD246 is the only white dwarf known that shows identifiable individual iron lines in the soft X-ray range. For the PG1159 star, a precise effective temperature determination is performed in order to confine the position of the blue edge of the GW Vir instability region in the HRD. Methods. The Chandra spectra are analyzed with chemically homogeneous as well as stratified NLTE model atmospheres that assume equilibrium between gravitational settling and radiative acceleration of chemical elements. Archival EUV and UV spectra obtained with EUVE, FUSE, and HST are utilized to support the analysis. Results. No metals could be identified in LB1919. All observations are compatible with a pure hydrogen atmosphere. This is in stark contrast to the vast majority of hot DA white dwarfs that exhibit light and heavy metals and to the stratified models that predict significant metal abundances in the atmosphere. For GD246 we find that neither stratified nor homogeneous models can fit the Chandra spectrum. The Chandra spectrum of PG1520+525 constrains the effective temperature to T-eff = 150 000 +/- 10 000 K. Therefore, this nonpulsating star together with the pulsating prototype of the GWVir class (PG 1159-035) defines the location of the blue edge of the GWVir instability region. The result is in accordance with predictions from nonadiabatic stellar pulsation models. Such models are therefore reliable tools to investigate the interior structure of GW Vir variables. Conclusions. Our soft X-ray study reveals that the understanding of metal abundances in hot DA white dwarf atmospheres is still incomplete. On the other hand, model atmospheres of hydrogen-deficient PG 1159-type stars are reliable and reproduce well the observed spectra from soft X-ray to optical wavelengths.
Chemical Abundances Of The Leo II Dwarf Galaxy
(2009-01) Shetrone, Matthew D.; Siegel, Michael H.; Cook, David O.; Bosler, Tammy; Shetrone, Matthew D.; Siegel, Michael H.
We use previously published moderate-resolution spectra in combination with stellar atmosphere models to derive the first measured chemical abundance ratios in the Leo II dwarf Spheroidal (dSph) galaxy. We find that for spectra with signal-to-noise ratio greater than 24, we are able to measure abundances from weak Ti, Fe, and Mg lines located near the calcium infrared triplet (CaT). We also quantify and discuss discrepancies between the metallicities measured from Fe I lines and those estimated from the CaT features. We find that while the most metal-poor ([Fe/H] < - 2.0]) Leo II stars have Ca and Ti abundance ratios similar to those of Galactic globular clusters, the more metal-rich stars show a gradual decline of Ti, Mg, and Ca abundance ratio with increasing metallicity. Finding these trends in this distant and apparently dynamically stable dSph galaxy supports the hypothesis that the slow chemical enrichment histories of the dSph galaxies is universal, independent of any interaction with the Milky Way. Combining our spectroscopic abundances with published broadband photometry and updated isochrones, we are able to approximate stellar ages for our bright red giant branch stars to a relative precision of 2-3 Gyr. While the derived age-metallicity relationship of Leo II hints at some amount of slow enrichment, the data are still statistically consistent with no enrichment over the history of Leo II.
Circumnuclear Molecular Gas In Megamaser Disk Galaxies NGC 4388 And NGC 1194
(2014-06) Greene, Jenny E.; Seth, Anil; Lyubenova, Mariya; Walsh, Jonelle; van de Ven, Glenn; Lasker, Ronald; Walsh, Jonelle
We explore the warm molecular and ionized gas in the centers of two megamaser disk galaxies using K-band spectroscopy. Our ultimate goal is to determine how gas is funneled onto the accretion disk, here traced by megamaser spots on sub-parsec scales. We present NIR IFU data with a resolution of similar to 50 pc for two galaxies: NGC 4388 with VLT/SINFONI and NGC 1194 with Keck/OSIRIS+AO. The high spatial resolution and rich spectral diagnostics allow us to study both the stellar and gas kinematics as well as gas excitation on scales only an order of magnitude larger than the maser disk. We find a drop in the stellar velocity dispersion in the inner similar to 100 pc of NGC 4388, a common signature of a dynamically cold central component seen in many active nuclei. We also see evidence for noncircular gas motions in the molecular hydrogen on similar scales, with the gas kinematics on 100 parsec scales aligned with the megamaser disk. In contrast, the high ionization lines and Br gamma trace outflow along the 100 parsec-scale jet. In NGC 1194, the continuum from the accreting black hole is very strong, making it difficult to measure robust two-dimensional kinematics, but the spatial distribution and line ratios of the molecular hydrogen and Br gamma have consistent properties between the two galaxies.
Dependence Of Nebular Heavy-Element Abundance On Hi Content For Spiral Galaxies
(2013-08) Robertson, Paul; Shields, Gregory A.; Dave, Romeel; Blanc, Guillermo A.; Wright, Audrey; Robertson, Paul; Shields, Gregory A.; Wright, Audrey
We analyze the galactic Hi content and nebular log(O/H) for 60 spiral galaxies in the Moustakas et al. (2006a) spectral catalog. After correcting for the mass-metallicity relationship, we show that the spirals in cluster environments show a positive correlation for log(O/H) on DEF, the galactic Hi deficiency parameter, extending the results of previous analyses of the Virgo and Pegasus I clusters. Additionally, we show for the first time that galaxies in the field obey a similar dependence. The observed relationship between Hi deficiency and galactic metallicity resembles similar trends shown by cosmological simulations of galaxy formation including inflows and outflows. These results indicate the previously observed metallicity-DEF correlation has a more universal interpretation than simply a cluster's effects on its member galaxies. Rather, we observe in all environments the stochastic effects of metal-poor infall as minor mergers and accretion help to build giant spirals.
A Detection Of H Alpha In An Exoplanetary Exosphere
(2012-06) Jensen, Adam G.; Redfield, Seth; Endl, Michael; Cochran, William D.; Koesterke, Lars; Barman, Travis; Endl, Michael; Cochran, William D.; Koesterke, Lars
We report on a search for H alpha absorption in four exoplanets. Strong features at H alpha are observed in the transmission spectra of both HD 189733b and HD 209458b. We attempt to characterize and remove the effects of stellar variability in HD 189733b, and along with an empirical Monte Carlo test the results imply a statistically significant transit-dependent feature of (-8.72 +/- 1.48) x 10(-4) integrated over a 16 angstrom band relative to the adjacent continuum. We interpret this as the first detection of this line in an exoplanetary atmosphere. A previous detection of Ly alpha in HD 189733b's atmosphere allows us to calculate an excitation temperature for hydrogen, T-exc = 2.6 x 10(4) K. This calculation depends significantly on certain simplifying assumptions. We explore these assumptions and argue that T-exc is very likely much greater than the radiative equilibrium temperature (the temperature the planet is assumed to be at based on stellar radiation and the planetary distance) of HD 189733b. A large T-exc implies a very low density that is not in thermodynamic equilibrium with the planet's lower atmosphere. We argue that the n = 2 hydrogen required to cause H alpha absorption in the atmosphere is created as a result of the greater UV flux at HD 189733b, which has the smallest orbit and most chromospherically active central star in our sample. Though the overall integration of HD 209458b's transmission spectrum over a wide band is consistent with zero, it contains a dramatic, statistically significant feature in the transmission spectrum with reflectional symmetry. We discuss possible physical processes that could cause this feature. Our remaining two targets (HD 147506b and HD 149026b) do not show any clear features, so we place upper limits on their H alpha absorption levels.
Discovery of Seven Companions To Intermediate-Mass Stars With Extreme Mass Ratios in the Scorpius-Centaurus Association
(2015-06) Hinkley, S.; Kraus, Adam L.; Ireland, Michael J.; Cheetham, Anthony; Carpenter, John M.; Tuthill, Peter; Lacour, Sylvestre; Evans, Thomas M.; Haubois, Xaubois; Kraus, Adam L.
We report the detection of seven low-mass companions to intermediate-mass stars (SpT B/A/F; M similar to 1.5-4.5M(circle dot)) in the Scorpius-Centaurus (Sco-Cen) Association using nonredundant aperture masking interferometry. Our newly detected objects have contrasts Delta L' approximate to 4-6, corresponding to masses as low as similar to 20 M-Jup and mass ratios of q approximate to 0.01-0.08, depending on the assumed age of the target stars. With projected separations rho approximate to 10-30 AU, our aperture masking detections sample an orbital region previously unprobed by conventional adaptive optics imaging of intermediate-mass Sco-Cen stars covering much larger orbital radii (similar to 30-3000 AU). At such orbital separations, these objects resemble higher-mass versions of the directly imaged planetary mass companions to the 10-30 Myr, intermediate-mass stars HR 8799, beta Pictoris, and HD 95086. These newly discovered companions span the brown dwarf desert, and their masses and orbital radii provide a new constraint on models of the Formation of low-mass stellar and substellar companions to intermediate-mass stars.
Discovery of the Transiting Planet Kepler-5B
(2010-04) Koch, David G.; Borucki, William J.; Rowe, Jason F.; Batalha, Natalie M.; Brown, Timothy M.; Caldwell, Douglas A.; Caldwell, John; Cochran, William D.; DeVore, Edna; Dunham, Edward W.; Dupree, Andrea K.; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ron L.; Howell, Steve B.; Jenkins, Jon M.; Latham, David W.; Lissauer, Jack J.; Marcy, Geoff W.; Morrison, David; Tarter, Jill; Cochran, William D.
We present 44 days of high duty cycle, ultra precise photometry of the 13th magnitude star Kepler-5 (KIC 8191672, T(eff) = 6300 K, log g = 4.1), which exhibits periodic transits with a depth of 0.7%. Detailed modeling of the transit is consistent with a planetary companion with an orbital period of 3.548460 +/- 0.000032 days and a radius of 1.431(-0.052)(+0.041) R(J). Follow-up radial velocity measurements with the Keck HIRES spectrograph on nine separate nights demonstrate that the planet is more than twice as massive as Jupiter with a mass of 2.114(-0.059)(+0.056) M(J) and a mean density of 0.894 +/- 0.079 g cm(-3).
The Dynamical Masses, Densities, And Star Formation Scaling Relations Of Ly Alpha Galaxies
(2014-01) Rhoads, James E.; Malhotra, Sangeeta; Richardson, Mark L. A.; Finkelstein, Steven L.; Fynbo, Johan P. U.; McLinden, Emily M.; Tilvi, Vithal S.; Finkelstein, Steven L.; McLinden, Emily M.
We present the first dynamical mass measurements for Ly alpha galaxies at high redshift, based on velocity dispersion measurements from rest-frame optical emission lines and size measurements from Hubble Space Telescope imaging, for nine galaxies drawn from four surveys. We use these measurements to study Ly alpha galaxies in the context of galaxy scaling relations. The resulting dynamical masses range from 109 to 10(10) M-circle dot. We also fit stellar population models to our sample and use them to place the Ly alpha sample on a stellar mass versus line width relation. The Ly alpha galaxies generally follow the same scaling relation as star-forming galaxies at lower redshift, although, lower stellar mass fits are also acceptable in similar to 1/3 of the Ly alpha galaxies. Using the dynamical masses as an upper limit on gas mass, we show that Ly alpha galaxies have unusually active star formation for their gas mass surface density. This behavior is consistent with what is observed in starburst galaxies, despite the typically smaller masses and sizes of the Ly alpha galaxy population. Finally, we examine the mass densities of these galaxies and show that their future evolution likely requires dissipational ("wet") merging. In short, we find that Ly alpha galaxies are low-mass cousins of larger starbursts.
Elemental Abundances Of Solar Sibling Candidates
(2014-06) Ramirez, Ivan; Bajkova, A. T.; Bobylev, V. V.; Roederer, Ian U.; Lambert, David L.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.; Wittenmyer, Robert A.; Bajkova, A. T.; Lambert, David L.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.
Dynamical information along with survey data on metallicity and in some cases age have been used recently by some authors to search for candidates of stars that were born in the cluster where the Sun formed. We have acquired high-resolution, high signal-to-noise ratio spectra for 30 of these objects to determine, using detailed elemental abundance analysis, if they could be true solar siblings. Only two of the candidates are found to have solar chemical composition. Updated modeling of the stars' past orbits in a realistic Galactic potential reveals that one of them, HD 162826, satisfies both chemical and dynamical conditions for being a sibling of the Sun. Measurements of rare-element abundances for this star further confirm its solar composition, with the only possible exception of Sm. Analysis of long-term high-precision radial velocity data rules out the presence of hot Jupiters and confirms that this star is not in a binary system. We find that chemical tagging does not necessarily benefit from studying as many elements as possible but instead from identifying and carefully measuring the abundances of those elements that show large star-to-star scatter at a given metallicity. Future searches employing data products from ongoing massive astrometric and spectroscopic surveys can be optimized by acknowledging this fact.
The Factory And The Beehive. II. Activity And Rotation In Praesepe And The Hyades
(2014-11) Douglas, S. T.; Agueros, M. A.; Covey, Kevin R.; Bowsher, E. C.; Bochanski, J. J.; Cargile, P. A.; Kraus, Adam; Law, N. M.; Lemonias, J. J.; Arce, Hector G.; Fierroz, D. F.; Kundert, A.; Kraus, Adam
Open clusters are collections of stars with a single, well-determined age, and can be used to investigate the connections between angular-momentum evolution and magnetic activity over a star's lifetime. We present the results of a comparative study of the relationship between stellar rotation and activity in two benchmark open clusters: Praesepe and the Hyades. As they have the same age and roughly solar metallicity, these clusters serve as an ideal laboratory for testing the agreement between theoretical and empirical rotation-activity relations at approximate to 600 Myr. We have compiled a sample of 720 spectra-more than half of which are new observations-for 516 high-confidence members of Praesepe; we have also obtained 139 new spectra for 130 high-confidence Hyads. We have also collected rotation periods (P-rot) for 135 Praesepe members and 87 Hyads. To compare H alpha emission, an indicator of chromospheric activity, as a function of color, mass, and Rossby number R-o, we first calculate an expanded set of chi values, with which we can obtain the H alpha to bolometric luminosity ratio, L-H alpha/L-bol, even when spectra are not flux-calibrated and/or stars lack reliable distances. Our. values cover a broader range of stellar masses and colors (roughly equivalent to spectral types from K0 to M9), and exhibit better agreement between independent calculations, than existing values. Unlike previous authors, we find no difference between the two clusters in their H alpha equivalent width or L-H alpha/L-bol distributions, and therefore take the merged H alpha and Prot data to be representative of 600 Myr old stars. Our analysis shows that H alpha activity in these stars is saturated for R-o <= 0.11(-0.03)(+0.02) Above that value activity declines as a power-law with slope beta = -0.73(-0.12,)(+0.06) before dropping off rapidly at Ro approximate to 0.4. These data provide a useful anchor for calibrating the age-activity-rotation relation beyond 600 Myr.
The Gentle Growth of Galaxies at High Redshifts in Overdense Environments
(2014-08) Romano-Diaz, Emilio; Shlosman, Issac; Choi, Jun-Hwan; Sadoun, Raphael; Shlosman, Issac
We have explored prevailing modes of galaxy growth for redshifts z similar to 6-14, comparing substantially overdense and normal regions of the universe, using high-resolution zoom-in cosmological simulations. Such rare overdense regions have been projected to host high-z quasars. We demonstrate that galaxies in such environments grow predominantly by a smooth accretion from cosmological filaments which dominates the mass input from major, intermediate, and minor mergers. We find that by z similar to 6, the accumulated galaxy mass fraction from mergers falls short by a factor of 10 of the cumulative accretion mass for galaxies in the overdense regions, and by a factor of 5 in the normal environments. Moreover, the rate of the stellar mass input from mergers also lies below that of an in situ star Formation (SF) rate. The fraction of stellar masses in galaxies contributed by mergers in overdense regions is similar to 12%, and similar to 33% in the normal regions, at these redshifts. Our median SF rates for similar to few x 10(9) M-circle dot galaxies agrees well with the recently estimated rates for z similar to 7 galaxies from Spitzer's SURF-UP survey. Finally, we find that the main difference between the normal and overdense regions lies in the amplified growth of massive galaxies in massive dark matter halos. This leads to the Formation of similar to 10(10) M-circle dot galaxies due to the similar to 100 fold increase in mass during the above time period. Such galaxies are basically absent in the normal regions at these redshifts.
Herschel Extreme Lensing Line Observations: Dynamics Of Two Strongly Lensed Star-Forming Galaxies Near Redshift Z=2
(2014-05) Rhoads, James E.; Malhotra, Sangeeta; Allam, Sahar; Carilli, Chris; Combes, Francoise; Finkelstein, Keely; Finkelstein, Steven L.; Frye, Brenda; Gerin, Maryvonne; Guillard, Pierre; Nesvadba, Nicole; Rigby, Jane; Spaans, Marco; Strauss, Michael A.; Finkelstein, Keely; Finkelstein, Steven L.
We report on two regularly rotating galaxies at redshift z approximate to 2, using high-resolution spectra of the bright [C II] 158 mu m emission line from the HIFI instrument on the Herschel Space Observatory. Both SDSS090122.37+181432.3 ("S0901") and SDSSJ120602.09+514229.5 ("the Clone") are strongly lensed and show the double-horned line profile that is typical of rotating gas disks. Using a parametric disk model to fit the emission line profiles, we find that S0901 has a rotation speed of nu sin(i) approximate to 120 +/- 7 kms(-1) and a gas velocity dispersion of sigma(g) < 23 km s-1 (1 sigma). The best-fitting model for the Clone is a rotationally supported disk having nu sin(i) approximate to 79 +/- 11 km s(-1) and sigma(g) less than or similar to 4 kms-1 (1 sigma). However, the Clone is also consistent with a family of dispersion-dominated models having sigma(g) = 92 +/- 20 km s (1). Our results showcase the potential of the [C II] line as a kinematic probe of high-redshift galaxy dynamics: [C II] is bright, accessible to heterodyne receivers with exquisite velocity resolution, and traces dense star-forming interstellar gas. Future [C II] line observations with ALMA would offer the further advantage of spatial resolution, allowing a clearer separation between rotation and velocity dispersion.
The HST/ACS Coma Cluster Survey. VIII. Barred Disk Galaxies In The Core Of The Coma Cluster
(2012-02) Marinova, Irina; Jogee, Shardha; Weinzirl, Tim; Erwin, Peter; Trentham, Neil; Ferguson, Henry C.; Hammer, Derek; den Brok, Mark; Graham, Alister W.; Carter, David; Balcells, Marc; Goudfrooij, Paul; Guzman, Rafael; Hoyos, Carlos; Mobasher, Bahram; Mouhcine, Mustapha; Peletier, Reynier F.; Peng, Eric W.; Kleijn, Gus V.; Marinova, Irina; Jogee, Shardha; Weinzirl, Tim
We use high-resolution (similar to 0.'' 1) F814W Advanced Camera for Surveys (ACS) images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z similar to 0.02 to study bars in massive disk galaxies (S0s), as well as low-mass dwarf galaxies in the core of the Coma cluster, the densest environment in the nearby universe. Our study helps to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. Our results are: (1) we characterize the fraction and properties of bars in a sample of 32 bright (M-V less than or similar to -18, M-* > 10(9.5) M-circle dot) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. We find that the measurement of a bar fraction among S0 galaxies must be handled with special care due to the difficulty in separating unbarred S0s from ellipticals, and the potential dilution of the bar signature by light from a relatively large, bright bulge. The results depend sensitively on the method used: the bar fraction for bright S0s in the Coma core is 50% +/- 11%, 65% +/- 11%, and 60% +/- 11% based on three methods of bar detection, namely, strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (the Coma core, A901/902, and Virgo) adopting the critical step of using matched samples and matched methods in order to ensure robust comparisons. We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation (within the error bars of +/- 11%) across environments which span two orders of magnitude in galaxy number density (n similar to 300-10,000 galaxies Mpc(-3)) and include rich and poor clusters, such as the core of Coma, the A901/902 cluster, and Virgo. We speculate that the bar fraction among S0s is not significantly enhanced in rich clusters compared to low-density environments for two reasons. First, S0s in rich clusters are less prone to bar instabilities as they are dynamically heated by harassment and are gas poor as a result of ram pressure stripping and accelerated star formation. Second, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We also take advantage of the high resolution of the ACS (similar to 50 pc) to analyze a sample of 333 faint (MV > -18) dwarf galaxies in the Coma core. Using visual inspection of unsharp-masked images, we find only 13 galaxies with bar and/or spiral structure. An additional eight galaxies show evidence for an inclined disk. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies or that any disks present are too hot to develop instabilities.
Inverting Color-Magnitude Diagrams To Access Precise Star Cluster Parameters: A New White Dwarf Age For The Hyades
(2009-05) Degennaro, Steven; von Hippel, Ted; Jefferys, William H.; Stein, Nathan; van Dyk, David; Jeffery, Elizabeth; Degennaro, Steven; von Hippel, Ted; Jefferys, William H.; Stein, Nathan; Jeffery, Elizabeth
We have extended our Bayesian modeling of stellar clusters-which uses main-sequence stellar evolution models, a mapping between initial masses and white dwarf (WD) masses, WD cooling models, and WD atmospheres-to include binary stars, field stars, and two additional main-sequence stellar evolution models. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. Under the assumption of a particular set of WD cooling models and atmosphere models, we estimate the age of the Hyades based on cooling WDs to be 648 +/- 45 Myr, consistent with the best prior analysis of the cluster main-sequence turnoff (MSTO) age by Perryman et al. Since the faintest WDs have most likely evaporated from the Hyades, prior work provided only a lower limit to the cluster's WD age. Our result demonstrates the power of the bright WD technique for deriving ages and further demonstrates complete age consistency between WD cooling and MSTO ages for seven out of seven clusters analyzed to date, ranging from 150 Myr to 4 Gyr.
Kepler-14B: A Massive Hot Jupiter Transiting An F Star in A Close Visual Binary
(2011-11) Buchhave, Lars A.; Latham, David W.; Carter, Joshua A.; Desert, Jean-Michel; Torres, Guillermo; Adams, Elisabeth R.; Bryson, Stephen T.; Charbonneau, David B.; Ciardi, David R.; Kulesa, Craig; Dupree, Andrea K.; Fischer, Debra A.; Fressin, Francois; Gautier, Thomas N., III; Gilliland, Ronald L.; Howell, Steve B.; Isaacson, Howard; Jenkins, Jon M.; Marcy, Geoffrey W.; McCarthy, Donald W.; Rowe, Jason F.; Batalha, Natalie M.; Borucki, William J.; Brown, Timothy M.; Caldwell, Douglas A.; Christiansen, Jessie L.; Cochran, William D.; Deming, Drake; Dunham, Edward W.; Everett, Mark; Ford, Eric B.; Fortney, Jonathan J.; Geary, John C.; Girouard, Forrest R.; Haas, Michael R.; Holman, Matthew J.; Horch, Elliott; Klaus, Todd C.; Knutson, Heather A.; Koch, David G.; Kolodziejczak, Jeffrey; Lissauer, Jack J.; Machalek, Pavel; Mullally, Fergal; Still, Martin D.; Quinn, Samuel N.; Seager, Sara; Thompson, Susan E.; Van Cleve, Jeffrey; Cochran, William D.
We present the discovery of a hot Jupiter transiting an F star in a close visual (0 ''.3 sky projected angular separation) binary system. The dilution of the host star's light by the nearly equal magnitude stellar companion (similar to 0.5 mag fainter) significantly affects the derived planetary parameters, and if left uncorrected, leads to an underestimate of the radius and mass of the planet by 10% and 60%, respectively. Other published exoplanets, which have not been observed with high-resolution imaging, could similarly have unresolved stellar companions and thus have incorrectly derived planetary parameters. Kepler-14b (KOI-98) has a period of P = 6.790 days and, correcting for the dilution, has a mass of M-p = 8.40(-0.34)(+ 0.35) M-J and a radius of R-p = 1.136(-0.054)(+ 0.073) R-J, yielding a mean density of rho(p) = 7.1 +/- 1.1 g cm(-3).
Kepler-4B: A Hot Neptune-Like Planet of A G0 Star Near Main-Sequence Turnoff
(2010-04) Borucki, William J.; Koch, David G.; Brown, Timothy M.; Basri, Gibor; Batalha, Natalie M.; Caldwell, Douglas A.; Cochran, William D.; Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ronald L.; Howell, Steve B.; Jenkins, Jon M.; Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Monet, David; Rowe, Jason F.; Sasselov, Dimitar; Cochran, William D.
Early time-series photometry from NASA's Kepler spacecraft has revealed a planet transiting the star we term Kepler-4, at R.A. = 19(h)02(m)27.(s)68, delta = +50 degrees 08'08 '' 7. The planet has an orbital period of 3.213 days and shows transits with a relative depth of 0.87 x 10(-3) and a duration of about 3.95 hr. Radial velocity (RV) measurements from the Keck High Resolution Echelle Spectrometer show a reflex Doppler signal of 9.3(-1.9)(+1.1) m s(-1), consistent with a low-eccentricity orbit with the phase expected from the transits. Various tests show no evidence for any companion star near enough to affect the light curve or the RVs for this system. From a transit-based estimate of the host star's mean density, combined with analysis of high-resolution spectra, we infer that the host star is near turnoff from the main sequence, with estimated mass and radius of 1.223(-0.091)(+0.053) M(circle dot) and 1.487(-0.084)(+0.071) R(circle dot).We estimate the planet mass and radius to be {M(P), R(P)} = {24.5 +/- 3.8 M(circle plus), 3.99 +/- 0.21 R(circle plus)}. The planet's density is near 1.9 g cm(-3); it is thus slightly denser and more massive than Neptune, but about the same size.
Kepler-7B: A Transiting Planet With Unusually Low Density
(2010-04) Latham, David W.; Borucki, William J.; Koch, David G.; Brown, Timothy M.; Buchhave, Lars A.; Basri, Gibor; Batalha, Natalie M.; Caldwell, Douglas A.; Cochran, William D.; Dunham, Edward W.; Furesz, Gabor; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ronald L.; Howell, Steve B.; Jenkins, Jon M.; Lissauer, Jack J.; Marcy, Geoffrey W.; Monet, David G.; Rowe, Jason F.; Sasselov, Dimitar D.; Cochran, William D.
We report on the discovery and confirmation of Kepler-7b, a transiting planet with unusually low density. The mass is less than half that of Jupiter, M(P) = 0.43 M(J), but the radius is 50% larger, R(P) = 1.48 R(J). The resulting density, rho(P) = 0.17 g cm(-3), is the second lowest reported so far for an extrasolar planet. The orbital period is fairly long, P = 4.886 days, and the host star is not much hotter than the Sun, T(eff) = 6000 K. However, it is more massive and considerably larger than the Sun, M(star) = 1.35 M(circle dot) and R(star) = 1.84R(circle dot), and must be near the end of its life on the main sequence.