Monday, May 23, 2011, 3:40 PM - 4:30 PM
118 Invited Session America Ballroom
118.01
Stellar Astrophysics from the Kepler Mission
Ronald L. Gilliland1
1STScI.
3:40 PM - 4:30 PM
America Ballroom
Through a qualitatively unique combination of both highly precise and nearly continuous multi-year, time-series photometry on 150,000 stars, Kepler is providing fundamentally new stellar astrophysics insights. In this talk I will introduce the characteristics of Kepler observations and results relevant to these studies. Some examples: (1) Stars like the Sun show low-amplitude acoustic oscillations. Kepler has provided better asteroseismic results for hundreds of solar-like stars than existed previously for only about 25 cases. (2) The recent detection of gravity mode oscillations excited in the deep interior of red giants, coupled with study of acoustic modes on the same stars is providing the meaningful constraints on stellar evolution theory long promised by asteroseismology. (3) On the timescale of several hours most relevant to the Kepler planet search program, we know from SOHO observations that the Sun varies by about 10 parts per million. Kepler is now providing measurements of this variability, with results averaging somewhat more than the Sun for thousands of stars. The era of ensemble studies of statistically robust samples of stars for asteroseismology and low-level variability possible previously only for the Sun has now begun.
Monday, May 23, 2011, 4:30 PM - 6:00 PM
119 Evolution of Galaxies I Oral Session America North
119.01
Galaxy Formation On A Moving Mesh: Technique And Global Baryonic Properties
Mark Vogelsberger1
1Harvard/CfA.
4:30 PM - 4:40 PM
America North
We present cosmological hydrodynamics simulations to study galaxy formation using the moving mesh code AREPO.
We introduce the simulations, numerical techniques and discuss results of the global baryon statistics.
Our simulations include primordial cooling taking into account photo-ionization due to
a spatially uniform UV background, a two-phase model to describe gas of the interstellar medium,
and a star formation method.
To contrast our results to previous calculations with a similar physics implementation, we repeat
all simulations with the well-tested SPH-code GADGET. Both codes
use an identical gravity solver and include the same sub-resolution physics, but use a completely different method to solve the inviscid Euler equations. This allows us to estimate the impact of hydro solver uncertainties
on the results of cosmological hydrodynamics calculations.
The global baryon statistics differ between the two simulation methods significantly. AREPO shows
systematically higher star formation rates, lower mean temperatures over the simulation volume and different
mass fractions in gas phases. Although both codes use the same cooling implementation, the cooling rates
in AREPO are larger than those in GADGET. These systematic differences demonstrate that inaccuracies in hydro solvers can lead to comparatively large uncertainties in the baryon characteristics.
119.02
Galaxy Formation on a Moving Mesh: Baryonic Properties of Galaxies and Halos
Dusan Keres1, M. Vogelsberger2, V. Springel3, L. Hernquist4
1Theoretical Astrophysics Center, UC Berkeley, 2ITC, Harvard, 3Heidelberg Institute for Theoretical Studies, Germany, 4Harvard University.
4:40 PM - 4:50 PM
America North
We present new type of cosmological hydrodynamic simulations to study formation of galaxies. Simulations were performed using newly developed
moving mesh code AREPO in a cosmological box evolved to z=0. We compare
the results from this new technique to the results from well-tested SPH code GADGET-3 which uses identical gravity solver, which enables to cleanly test the differences in hydrodynamics. We found several important, systematic differences in properties of galaxies and gaseous components of halos. These include significantly more extended disks and faster cooling of the hot halo gas in massive
halos in AREPO. Owing to hierarchical nature of halo and galaxy buildup these differences than propagate to many other properties of simulated halos and galaxies.
Given the advantages of hydrodynamic scheme in AREPO in idealized test problems, as well as tests we did in cosmological environment,
our new findings are questioning reliability of some the previous results based on SPH technique.
119.03D
Probing the Accretion of Gas onto Galaxies: Opportunities and Pitfalls
Claude-Andre Faucher-Giguere1
1University of California, Berkeley.
4:50 PM - 5:10 PM
America North
Galaxies must continuously accrete gas from the intergalactic medium in order to sustain their observed star formation rates. How this accretion proceeds is a fundamental problem in galaxy formation, as it determines how rapidly galaxies can grow as a function of mass and redshift, as well as the efficiency of feedback processes. While theoretical work predicts that galaxies acquire most of their baryons via the "cold mode", observations have so far not found clear traces of the cold streams. I will discuss results from a research program aimed at robustly quantifying the observational signatures of the cold mode, focusing on Ly-alpha emission and absorption and their connection to high-redshift "Ly-alpha blobs" and halo absorbers. In doing so, I will highlight some of the theoretical challenges involved, which can jeopardize this unique opportunity to test a physical prediction of galaxy formation if not addressed properly.
119.04
Ripples in Outer Gas Disks: A Calorimeter of Gravity
Sukanya Chakrabarti1
1Florida Atlantic University.
5:10 PM - 5:20 PM
America North
In recent papers, we have shown that analysis of observed disturbances in extended HI disks can be used to constrain the mass and current location of galactic satellites (Chakrabarti & Blitz 2009; Chakrabarti & Blitz 2011; Chakrabarti, Bigiel, Chang & Blitz 2011). This method, known as Tidal Analysis, was developed to characterize dark matter sub-structure and does not require any knowledge of the optical light from galactic satellites. Here, we explore the role of halo concentration and shape in producing these disturbances. Specifically, we investigate if disturbances in extended HI disks can be used as an observational probe of the concentration of the dark
matter halo of the primary galaxy. We also report recent results on the analysis of halo shapes on the production of disturbances in extended HI disks.
119.05
Star Formation Quenching in Hickson Compact Groups: Death by Debris?
Michelle E. Cluver1, P. Appleton2, J. Rasmussen3, U. Lisenfeld4, P. Guillard1, P. Ogle1, L. Verdes-Montenegro5, M. Yun6, T. Jarrett7, T. Bitsakis8, C. K. Xu2
1SSC, Caltech, 2NHSC, Caltech, 3Dark Cosmology Centre, Denmark, 4Universidad de Granada, Spain, 5Instituto de Astrofisica de Andalucia, Spain, 6University of Massachusetts, 7IPAC, Caltech, 8University of Crete, Greece.
5:20 PM - 5:30 PM
America North
Recent studies show that compact groups appear to follow an evolutionary sequence, linked to gas depletion, caused by interactions in the dense environment. In mid-infrared color-color space, galaxies in Hickson Compact Groups (HCGs) show a roughly bimodal separation into dusty, star forming and dust-free, evolved systems. This appears to correlate with HI-depletion, but not the presence of hot X-ray gas. We present results from our Spitzer spectroscopy study of a sample of 23 HCGs, where we find that galaxies with intermediate mid-infrared colors preferentially show enhanced warm H2 emission (i.e. not associated with star formation). We propose a hypothesis where group galaxies collide with previously stripped tidal material, thus producing shock-heated H2 emission. The evolution from gas-rich to gas-poor is accelerated due to galaxies experiencing stochastic heating and/or viscous stripping, which effectively shuts down star formation, causing them to move rapidly from actively star forming to passively evolving systems (i.e. dominated by an old stellar population).
119.06
A Multiwavelength Study of an Assembling Galaxy Cluster : AGN and Starburst Outflows
Emily E. Freeland1
1Texas A&M University.
5:30 PM - 5:40 PM
America North
Galaxy groups are increasingly recognized as a key environment for transforming galaxy morphologies and star formation rates. Current research is focused on illuminating specific physical processes responsible for galaxy evolution in these systems. Super-Group 1120-12 consists of four virialized groups at z~0.36 that will merge and form a cluster comparable in mass to Coma by the current epoch. Using multiwavelength (X-ray, UV, Optical, 24 micron, Radio) imaging and spectroscopic data we identify numerous AGN, starburst, and star-forming galaxies and characterize their associated outflows and physical properties in the context of the group environment.
120 Dark Matter & Dark Energy/Large Scale Structures, Cosmic Distance Scale Oral Session America Central
120.01D
Understanding Dark Matter Halos with Tidal Caustics
Robyn E. Sanderson1
1Kapteyn Institute, Netherlands.
4:30 PM - 4:50 PM
America Central
Recently, large-scale sky surveys and deep follow-up images have discovered a wealth of tidal debris around our Galaxy and others nearby. This debris can give clues to the shapes and masses of the dark matter haloes surrounding these galaxies, as well as those of the dwarf galaxies that were tidally disrupted to form the debris. The class of tidal features known variously as ``shells'' or ``umbrellas" comprises debris that has arisen from minor (high-mass-ratio) mergers with low orbital angular momentum; the nearly radial orbits of the debris give rise to a unique shape and a universal radial density profile. The profile takes this form because the dynamics of the debris can be described by a modified version of the mathematical theory of caustics. Based on this universality, I present a new method for constraining multiple parameters of a minor merger in an external galaxy using only the two-dimensional image of the debris.
120.02D
Influence of Multiple Deflections on Weak Lensing Measurements of Dark Matter Halo Shapes
Paul Howell1
1Boston Univ..
4:50 PM - 5:10 PM
America Central
Statistical weak gravitational lensing of background galaxy images by foreground galaxies is now a widely used and powerful tool to probe the distribution of galactic dark matter. However, such analysis often depends on an assumption of a single, weak deflection of the background rays by a foreground lensing object.
I will present results that demonstrate the importance of considering multiple deflections when interpreting weak shear results. In particular, I show that multiple deflections can introduce systematic depression of γ+ - the anisotropic shear with respect to the major axis of the lens, and a corresponding amplification of γ-. Such systematics can lead to reduced estimates of the degree of flattening of galaxy dark matter halos, or even the conclusion that dark matter halos are anti-aligned with the light.
I create two complimentary simulation spaces to explore these effects. One is a simple system consisting of a single lens whose dark matter halo shape and orientation are known. The subject lens is then embedded in an environment of masses distributed in redshift space. Apparent shear of background sources is found in the usual way and results are tabulated both using apparent lens shape and PA (as an observer would) and using actual shape and PA.
A second simulation space replicates as nearly as possible a real observational dataset. I use this simulation to help overcome the systematic effects introduced by multiple deflections to infer actual halo shapes. From this result, I make a modest (95%) detection of flattened dark matter halos aligned with the light and that an NFW type density profile is preferred (95%) over an isothermal density profile. Detection of an isotropic lensing signal as demanded by MOND is similarly excluded.
Support from the National Science Foundation under contract AST-0708468 is gratefully acknowledged.
120.03
Structure Formation Can Hint on the Quantum-mixed Nature of Dark Matter
Mikhail Medvedev1
1University of Kansas.
5:10 PM - 5:20 PM
America Central
What happens to a dark matter particle trapped in a static gravitational potential of a halo? The obvious answer that it will remain gravitationally bound forever appears to be not quite true for a quantum-mixed particle, like a neutralino, for example. We will show that the particle can gradually and irreversibly escape, or ``evaporate'', from the gravitational well --- the effect that has no counterpart in classical physics. This new effect is not related to the well-known processes such as flavor oscillations, particle decay, quantum tunneling, etc. Further, we investigated how quantum evaporation would affect the structure formation. It was found that the flavor-mixed dark matter model can simultaneously explain two outstanding problems of cosmology, namely the dark halo cusp problem and the sub-structure (the "missing satellites") problem.
[This work is supported by DE-FG02-07ER54940, AST-0708213, NNX-08AL39G.]
120.04
Measuring the 3D Clustering of Undetected Galaxies Through Cross Correlation of their Cumulative Flux Fluctuations from Multiple Spectral Lines
Eli Visbal1, A. Loeb1
1Harvard University.
5:20 PM - 5:30 PM
America Central
We discuss a method for detecting the emission from high redshift galaxies by cross correlating flux fluctuations from multiple spectral lines. If one can fit and subtract away the continuum emission with a smooth function of frequency, the remaining signal contains fluctuations of flux with frequency and angle from line emitting galaxies. Over a particular small range of observed frequencies, these fluctuations will originate from sources corresponding to a series of different redshifts, one for each emission line. It is possible to statistically isolate the fluctuations at a particular redshift by cross correlating emission originating from the same redshift, but in different emission lines. This technique will allow detection of clustering fluctuations from the faintest galaxies which individually cannot be detected, but which contribute substantially to the total signal due to their large numbers. We describe these fluctuations quantitatively through the line cross power spectrum. As an example of a particular application of this technique, we calculate the signal-to-noise ratio for a measurement of the cross power spectrum of the OI(63 micron) and OIII(52 micron) fine structure lines with the proposed Space Infrared Telescope for Cosmology and Astrophysics. We find that the cross power spectrum can be measured beyond a redshift of z=8. Such observations could constrain the evolution of the metallicity, bias, and duty cycle of faint galaxies at high redshifts and may also be sensitive to the reionization history through its effect on the minimum mass of galaxies. As another example, we consider the cross power spectrum of CO line emission measured with a large ground based telescope like CCAT and 21-cm radiation originating from hydrogen in galaxies after reionization with an interferometer similar in scale to MWA, but optimized for post-reionization redshifts.
120.05
The Halo Occupation Distribution of Active Galactic Nuclei
Suchetana Chatterjee1, D. Nagai1, J. Richardson1, Z. Zheng1, C. Degraf2, T. DiMatteo2
1Yale University, 2Carnegie Mellon University.
5:30 PM - 5:40 PM
America Central
We investigate the halo occupation distribution of active galactic nuclei (AGN) using a state-of-the-art cosmological hydrodynamic simulation that self-consistently incorporates the growth and feedback of supermassive black holes and the physics of galaxy formation (DiMatteo et al.\ 2008). We show that the mean occupation function can be modeled as a softened step function for central AGN and a power law for the satellite population. The satellite occupation is consistent with weak redshift evolution and a power law index of unity. The number of satellite black holes at a given halo mass follows a Poisson distribution. We show that at low redshifts (z=1.0) feedback from AGN is responsible for higher suppression of black hole growth in higher mass halos. This effect introduces a bias in the correlation between instantaneous AGN luminosity and the host halo mass, making AGN clustering depend weakly on luminosity at low redshifts. We show that the radial distribution of AGN follows a power law which is fundamentally different from those of galaxies and dark matter. The best-fit power law index is -2.26 ± 0.23. The power law exponent do not show any evolution with redshift, host halo mass and AGN luminosity within statistical limits. Incorporating the environmental dependence of supermassive black hole accretion and feedback, our formalism provides the most complete theoretical tool for interpreting current and future measurements of AGN clustering.
121 Stars, Dwarfs, Stellar, Circumstellar Disks Oral Session America South
121.01
Large Ampltiude, Quasi-Periodic Variability of a Cool Brown Dwarf
Jacqueline Radigan1, R. Jayawardhana1, D. Lafreniere2, E. Artigau2
1University of Toronto, Canada, 2Universite de Montreal, Canada.
4:30 PM - 4:40 PM
America South
We present continuous photometric monitoring of an early T-type brown dwarf in the near-infrared. Observations over 7 nights indicate that the target is variable with a period of ~7.7 hours and peak-to-peak amplitudes of up to 30% in the J band, the largest ever reported for a field brown dwarf. The evolving nature of the light curve, which displays phase changes in multi-epoch observations over months, suggests that atmospheric surface features --most likely heterogeneous clouds---are responsible. We also discuss our attempts to use combinations of current 1D 'cloudy' and 'clear' model atmospheres to reproduce simultaneously both the J, H, Ks light curve amplitudes as well as the target's observed spectral energy distribution. This object joins the T2.5 dwarf SIMP0136 discovered by Artigau and coworkers as the second L/T transition brown dwarf to display large-amplitude variability on rotational timescales, suggesting that the fragmentation of dust clouds at the L/T transition may contribute to the abrupt decline in condensate opacity and J-band brightening observed to occur over this regime. Furthermore, the presence of discrete, long-lived cloud features on these objects offers the potential to map evolving weather patterns, and hence extend studies of atmospheric circulation beyond our solar system, to a substellar mass regime never before probed.
121.02
Substellar Objects in Nearby Young Clusters (SONYC): Latest Results
Ray Jayawardhana1, K. Muzic1, A. Scholz2, V. Geers3, M. Tamura4
1University of Toronto, Canada, 2Dublin Institute for Advanced Studies, Ireland, 3ETH, Switzerland, 4National Astronomical Observatory of Japan, Japan.
4:40 PM - 4:50 PM
America South
The origins and characteristics of the lowest mass free-floating objects constitute a major question in the study of star and planet formation. Our on-going SONYC (Substellar Objects in Nearby Young Clusters) survey uses extremely deep wide-field optical and near-infrared imaging, with follow-up spectroscopy on 8m-class telescopes, in combination with Spitzer photometry to explore substellar objects with masses down to a few times that of Jupiter. Here we present our latest findings for three nearby star-forming regions (NGC 1333, rho Oph and Cha I), describe the lowest mass objects we have found so far, and discuss the minimum mass limit for star formation.
121.03
DASCH Photometry Of KU Cygni: An 8-yr Dimming Around 1900
Sumin Tang1, J. Grindlay1, E. Los1, M. Servillat1
1Harvard-Smithsonian Center for Astrophysics.
4:50 PM - 5:00 PM
America South
KU Cygni is an Algol-type eclipsing binary consisted of a F-type main sequence star (gainer) with a large accretion disk, and a K5III red giant (donor). Here we present the discovery of an 8-yr dimming begining in 1895 found from its 100 yr DASCH light curve. It showed a 0.7 mag slow dimming from 1895 to 1903, and then quickly brightened back to normal state in 1903. After 1903, KU Cygni was stable within 0.2 mag in non-eclipsing phases when our data are available (i.e. 1909-1952 and 1962-1990). The dimming event is probably caused by increases in dust extinction surrounding the gainer, and the quick brightening could be due to the evaporation of dust transported inwards through the disk surrounding the gainer. The dust excess during the dimming event might arise from clumps of dusty gas ejected from the red giant donor.
121.04
Resolving The CO Snow Line In The Disk Around HD 163296
Chunhua Qi1, P. D'Alessio2, K. I. Öberg1, D. J. Wilner1, A. M. Hughes1, S. A. Andrews1, S. Ayala2
1Harvard Smithsonian, CfA, 2Universidad Nacional Autonóma de México, Mexico.
5:00 PM - 5:10 PM
America South
We report Submillimeter Array (SMA) observations of multiple lines of CO (J=2-1, 3-2 and 6-5) and CO isotopologues (13CO J=2-1, C18O J=2-1 and C17O J=3-2) in the disk around the Herbig Ae star HD 163296 at ~ 2 arcsec (250 AU) resolution, and we interpret these data in the framework of a model that constrains
the radial and vertical location of the line emission regions. We first develop a set of physically self-consistent accretion disk models with exponentially tapered edges that reproduces the observed spectral energy distribution and spatially resolved millimeter dust continuum emission. We further constrain the vertical structure of the model, taking advantage of the wide range of excitation sampled by the multiple optically thick CO lines, in particular the rarely observed J=6-5 line. The resulting model has a cold midplane populated by large grains with a large scale height. Using this model, we fit
for the location of the optically thinner CO isotopologue line emissions
and find they are confined between two vertical boundaries: a lower boundary around 19 K (due to CO freeze-out) and an upper boundary where the surface density is around 1021 cm-2 (due to photodissociation). If all CO isotopologues freeze out at 19 K, then we find isotopic ratios of 12C/13C, 16O/18O and 18O/17O consistent with the quiescent interstellar gas-phase values. We discuss the relevance of the CO freeze-out on the determination of the
fractional abundances of CO and its isotopologues.
121.05
Resolving the Cepheid Mass Discrepancy with Pulsation-Driven Mass Loss
Hilding Neilson1, M. Cantiello1, N. Langer1
1University of Bonn, Germany.
5:10 PM - 5:20 PM
America South
The Cepheid Mass Discrepancy is the difference between mass predictions using stellar evolution and stellar pulsation calculations. Currently, masses from stellar pulsation are typically 10-20% smaller than those from evolution models. This problem is a challenge for the understanding of stellar evolution and pulsation. One potential solution is enhanced mass loss during the Cepheid stage of evolution. We use state-of-the-art stellar evolution models and find that the combination of moderate convective core overshooting and pulsation-driven mass loss resolves the Cepheid Mass Discrepancy.
121.06
Linear Polarization Light Curves of Oblique Magnetic Rotators
Richard Ignace1, K. T. Hole1, J. P. Cassinelli2, G. D. Henson1
1East Tennessee State Univ., 2University of Wisconsin.
5:20 PM - 5:30 PM
America South
The quality and quantity of polarimetric data being collected for stellar sources creates new opportunities for studying stellar properties and evolution, and also leads to new challenges for modeling and interpreting such data. Inspired by fresh prospects for detecting the Hanle effect to study photospheric magnetic fields, we have focused attention on purely geometrical aspects for polarimetric variability in the example of oblique magnetic rotators. In the case of axisymmetric fields, we highlight two key facts: (a) polarimetric lightcurves necessarily exhibit a certain time symmetry with rotation phase, and (b) variations in the polarization position angle can be modeled based on geometrical projection effects, independent of the photospheric magnetic field. These conclusions also have general applicability, such as to Thomson scattering and the transverse Zeeman effect. The authors gratefully acknowledge that funding for this work was provided by the National Science Foundation, grant AST-0807664.
122 Binary Stellar Systems, X-ray Binaries Oral Session St. George CD
122.01
Using Black Hole--Pulsar Binaries to Search for a Warped Extra Dimension
Michael Kavic1, J. Simonetti2, D. Minic2
1The College of New Jersey, 2Virginia Tech.
4:30 PM - 4:40 PM
St. George CD
We will discuss the observable effects of enhanced black-hole mass loss in a black hole--neutron star (BH--NS) binary, due to the presence of a warped extra spatial dimension in the braneworld scenario. For some masses and orbital parameters in the expected ranges the binary components would outspiral, the opposite of the behavior due to energy loss from gravitational radiation alone. If the NS is a pulsar, observations of the rate of change of the orbital period with a precision obtained for the Binary Pulsar B1913+16 could easily detect the effect of mass loss. Observations of a BH--pulsar system could set considerably better limits on these braneworld models than could be determined by torsion-balance gravity experiments in the foreseeable future.
122.02
Chandra Watches Over A Decade Of Variability In M31 Globular Clusters
Robin Barnard1, Z. Li1, M. Garcia1, S. Murray2
1Harvard-Smithsonian Center for Astrophysics, 2Johns Hopkins University.
4:40 PM - 4:50 PM
St. George CD
The central region of M31 has been monitored with Chandra > 120 times over the last ~11 years. In this region we find X-ray sources corresponding to 35 out of ~420 globular clusters; these are highly likely to be X-ray binaries. We have created long-term, calibrated lightcurves for all 35 sources, and will present highlights of our variability survey. We have detected significant variability in all the sources with 0.3-10 keV luminosity > ~2x10E+36 erg/s. Since the emission spectra of background active galaxies often resemble those of X-ray binaries, the long term variability will be a valuable tool for identifying X-ray binaries in the remaining 400 sources in our field. This work is funded by Chandra grant GO9-0100X and HST grant GO-1101.
122.03
The intriguing Case of the New Supergiant Fast X-Ray Transient Class: An Update
Pietro Ubertini1, L. Sidoli2, A. Bazzano1, V. Sguera3
1INAF/IASF-Roma, Italy, 2INAF/IASF-Milano, Italy, 3INAF/IASF-Bologna, Italy.
4:50 PM - 5:00 PM
St. George CD
Supergiant Fast X-ray Transients (SFXTs) are an intriguing subclass of High Mass X-ray Binaries hosting a blue supergiant companion. They display brief outbursts composed by bright flares lasting a few thousands seconds, during which an X-ray luminosity of 1E36-1E37 erg/s is reached. Their extreme X-ray variability, with a dynamic range of 3 to 5 orders of magnitudes from quiescence to the outburst peak, is still a matter of debate: in massive binaries where the compact object should be embedded all the time within the strong wind from the supergiant companion, a transient X-ray emission is very difficult to explain. The determination of pulse and orbital periodicities are crucial to cast light on the outburst mechanism and on the evolutionary status of these X-ray binaries. The number of SFXTs where X-ray periodicities have been discovered is indeed continuously growing thanks to timing analysis of large datasets, especially from INTEGRAL/IBIS and Swift/BAT. We will review the most recently found periodicities and their important implications for the physical mechanisms proposed to explain the SFXTs outbursts.
122.04
Observing Mass Transfer in a Neglected Interacting Binary Star
Phillip A. Reed1
1Kutztown University.
5:00 PM - 5:10 PM
St. George CD
The eclipsing and interacting binary star R Arae is a very interesting system that has unfortunately been neglected. The few spectroscopic studies of the system report badly blended absorption lines that indicate mass transfer, but until now there has been no orbital period study to conclusively show a real period change resulting from mass transfer. In this study, new data are combined with those found in the available literature and in the database of the American Association of Variable Star Observers to construct the first ephemeris curve for R Ara, which spans more than a century since its discovery in 1894. Average orbital period change and conservative mass transfer rates are presented.
122.05
Magnetospheric Accretion Shocks In The X-ray Spectrum Of The Ultra-compact Binary 4u 1626-67
Norbert S. Schulz1, H. L. Marshall1, D. Chakrabarty1
1MIT.
5:10 PM - 5:20 PM
St. George CD
In 2008 the ultra-compact binary pulsar underwent another episode of torque reversal since the one in the early 1990s. We observed the X-ray source one year after the event with the HETG spectrometer onboard Chandra. While the light curve before torque reversal is featureless, it now shows enhanced flaring similar to observations before the first reversal episode. The X-ray continuum is fit by the same spectral model as before, but exhibits significantly larger blackbody temperatures
and smaller emission radii. The spectrum for the first time shows a narrow Fe K fluorescence line.
We show while a photo-ionized plasma cannot fit the Ne and O Doppler line emissions, a collisionally ionized plasma provides a better description of the data. We propose, that the nature of the Doppler line pairs can then be described as magnetospheric
accretion shocks and shoked matter moving towards the magnetospheric poles.
122.06
Distribution And Nature Of The Accretion-powered Binaries In The Galactic Center Region From The Chandra BLS
Jonathan E. Grindlay1, J. Hong1, M. Servillat1, P. Zhao1, B. Allen1, M. van den Berg2
1Harvard-Smithsonian, CfA, 2Utrecht University, Netherlands.
5:20 PM - 5:30 PM
St. George CD
We have completed the analysis of the Chandra Bulge Latitude Survey (BLS), a close-tiled mosaic of 36 ACIS-I fields obtained with Chandra in cycles 7 - 9 and covering (l, b) ~ +/-0.3, +/-1.4deg. With 15ksec exposures per field, some 2500 sources are detected, with luminosities Lx(0.3-8keV) >~10^32 erg/s. This survey maps the latitude distribution of the galactic center region (GCR) sources for comparison with the longitude distribution of the Wang et al (2002) survey. The BLS extends below the plane to (just) include the "Limiting Window" field (b = -1.3deg, the closest low extinction window to SgrA* with Av ~4) we originally observed in a 100ksec pointing and which was recently observed in a much deeper pointing by Revnivtsev et al to study the Galactic Ridge. From our optical (VRI; CTIO-4m/Mosaic) and nIR (JHK; CTIO-4m/ISPI) images, we identify foreground sources and constrain the Bulge sources to not be wind-fed high mass systems. By selecting on sources detected in the Hard (>2keV) but not in the Soft (<2keV) bands, we can reject foreground sources and measure the latitude and projected radial distributions of the hard sources in the GCR that are likely dominated by accreting white dwarfs (CVs) but also include quiescent low mass X-ray binaries (qLMXBs). And from comparison with the Wang survey, the combined radial distribution of Lx ~10^32-33 erg/s hard sources in the GCR, which are dominated by accreting compact objects in binaries, is derived for comparison with models of the Bulge and its formation history.
122.07
An Experimental Approach to Population Synthesis of Hot Subdwarf Stars in Binaries
Drew R. Clausen1, R. A. Wade1, R. K. Kopparapu1, R. O'Shaughnessy2
1The Pennsylvania State University, 2University of Wisconsin Milwaukee.
5:30 PM - 5:40 PM
St. George CD
We use the BSE code (Binary Stellar Evolution) of Hurley et al. (2002) to explore the binary formation channels of subdwarf B (sdB) stars, varying parameters that control mass and angular momentum loss from the system, whether or not mass transfer is stable, common envelope ejection efficiency, and the helium ignition point. We choose a large number of plausible initial binary masses and orbital periods (M1, M2, P) by Monte Carlo and follow the evolution of each binary to determine whether an sdB is produced. Sampling our database of simulations uniformly in time, we estimate the "present-day" distribution of sdB binaries with non-degenerate companions. We find that the distributions of periods and companion masses are extremely sensitive to changes in these parameters, and that reproducing the results of previous binary population synthesis studies related to hot subdwarfs requires modifying many assumptions hardwired into BSE. Our models suggest that observations of sdB-F dwarf binaries can constrain the critical mass ratio for stable mass transfer from red giants or α_CE.
Partial Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number TM8-9007X issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060, with additional support from NASA grant NNX09AC83G.
122.08
Status Report on a Search for F stars with Hidden Hot Subdwarf Companions
Richard A. Wade1, D. R. Clausen1, M. A. Stark2, C. V. Griffith1
1Penn State Univ., 2Univ. Michigan/Flint.
5:40 PM - 5:50 PM
St. George CD
Observations to date preferentially find Galactic hot subdwarf (sdB/sdO) stars in binaries when the subdwarfs are paired with relatively faint companions (G/K/M dwarfs, white dwarfs). This selection bias may distort our perspective of the evolutionary channels that form hot subdwarfs in the galactic disk. A predicted and possibly more numerous population of binaries features a lower-mass, lower-luminosity, longer-lived hot subdwarf hiding in the glare from its brighter companion: the subdwarf + A/early F binaries. Such systems may arise when mass transfer is initiated in the Hertzsprung gap.
A survey is underway at Penn State to identify hot subdwarfs paired with early F stars, determine their properties, and establish their space density. The project makes use of ground and space archival data to identify these systems (from their UV excesses) and new spectroscopic observations to refine the sample and determine their orbital periods and other properties. Successful characterization of this group of close binaries should help to challenge, calibrate, or refine models of binary star evolution that are used in population synthesis studies. The motivation, methodology, and status of this search for hidden hot subdwarfs will be presented.
This study makes use of NASA archival data from 2MASS and GALEX. Support from NASA grant NNX09AC83G and NSF grant AST-0908642 is gratefully acknowledged. Observations carried out at KPNO and Hobby-Eberly Telescope.
123 Quasars, AGN, Starbursts, and SEDs Oral Session Staffordshire
123.01
Orientation Effects in the Spectral Energy Distributions of High-z 3CRR Sources Including New Far-IR Herschel Data.
Joanna Kuraszkiewicz1, B. Wilkes1, P. Barthel2, M. Haas3, S. Willner1, C. Leipski4, M. Ashby1, G. Fazio1
1Harvard-Smithsonian, CfA, 2Kapteyn Institute, Netherlands, 3Astronomisches Institut, Ruhr-University, Germany, 4MPIA, Germany.
4:30 PM - 4:40 PM
Staffordshire
A critical problem in understanding AGN and their contribution to the accretion power of the Universe is deducing their intrinsic properties from the observed properties, which are highly orientation/obscuration dependent. One way to select AGN samples that are unbiased by the effects of orientation/obscuration is low-frequency radio emission. Here we study a complete, 178 MHz radio flux-limited, orientation unbiased sample of 3CRR sources with high-redshift (1 < z < 2). At these redshifts the radio luminosities of the 3CRR sources are high ensuring that all sources in the sample are AGN. The sample includes 20 quasars and 18 radio galaxies, thought to be AGN viewed edge-on according to unification models. The estimate of orientation is provided by the radio core dominance. We have begun studies of the Chandra X-ray and Spitzer IR properties and their dependence on orientation. Here we extend these studies by compiling full (radio-to-X-ray) spectral energy distributions (SEDs)complementing the Chandra and Spitzer data with existing data from the literature and astronomical databases. Until recently one crucial gap remained in our multi-wavelength SED coverage: the far-infrared, which is emitted by dust and is key to measuring star formation in our sources. ESA's newly operating `cornerstone' mission, Herschel, is the first observatory to cover the 60-670um (observed frame) range. We show for the first time the full SEDs of the high-z 3CRR sources
including the new, complementary Herschel data. We present preliminary results of our study of the dependence of the SEDs on orientation (the 3CRR sources span a full range of inclination angles) and disentangle orientation effects from other effects (such as e.g. accretion rate).
123.02
Eddington Ratios Of Obscured GOODS AGN at 0.5
Brooke Simmons1, C. M. Urry1, J. Van Duyne2, A. M. Koekemoer3, N. A. Grogin3
1Yale Univ., 2Northrup Grumman, 3Space Telescope Science Institute.
4:40 PM - 4:50 PM
Staffordshire
Using a new method for calculating bolometric luminosities, we examine the Eddington ratios of a sample of 87 X-ray-selected obscured AGN in the GOODS fields. We find that the black holes in the sample span three orders of magnitude in mass, from 4e6 to 6e9 solar masses (median value 6e8), where the masses are estimated using bulge luminosities of the host galaxies. The majority of these AGN have Eddington ratios below 1%, and we detect no evolution in the mean Eddington ratio out to z=1.25. This implies that the bulk of black hole growth in these obscured AGN must have occurred at z>1 and that we are observing them in a slow- or no-growth state.
Our bolometric luminosities, based on dust-corrected central point-source SEDs, have a smaller spread than do alternative estimates from corrections to the X-ray luminosity or direct SED integration, suggesting our new method yields a better measure of bolometric luminosity; these values also agree with theoretical models of AGN luminosity based on a unification scenario.
123.03
Building Up the Red-Sequence: The AGN-Starburst Connection
Laura Trouille1, C. Tremonti2, R. Hickox3
1Northwestern University CIERA Postdoctoral Fellow, 2University of Wisconsin - Madison, 3Durham, United Kingdom.
4:50 PM - 5:00 PM
Staffordshire
Post-starburst galaxies, also known as K+A or E+A galaxies because of the characteristic features in their spectra, have recently undergone an abrupt cessation of active star formation (within 20-500 Myr). This exceptional and rare stage in galaxy evolution is thought to occur during the transition from gas-rich, star-forming galaxies into early-types. While it is poorly understood what causes the abrupt end of their star formation, there is strong evidence that galaxy-galaxy tidal interactions or mergers trigger the starburst in many of these galaxies. This same mechanism for triggering intensive star formation may also cause strong fuelling onto a central supermassive black hole. By studying the evolution of the properties of post-starbursts, we obtain insights into the origin of the red-sequence and key properties of the AGN-starburst connection.
The use of post-starbursts as probes is only now feasible with the advent of large optical spectroscopic surveys. Here we compare results from the ~3000 SDSS DR7 post-starbursts at z~0.1 (for which ~60 have associated archival Chandra data) and the ~200 post-starbursts from the DEEP2, zCOSMOS, and OPTX surveys at z~0.9 (accompanied by deep Chandra imaging). A key benefit of studying post-starburst galaxies is that they are natural chronometers; detailed population synthesis modeling provides an estimate of the time since the peak star-formation event. In this study we address the following questions: 1) Does a visual inspection for near-neighbors and tidal disruptions in our low-redshift sample show a trend with post-starburst age? 2) Do post-starbursts move across optical emission-line diagnostic diagrams as they age and what does this tell us about the time-delay between starburst activity and AGN fueling? 3) Are post-starburst X-ray properties (for individually detected sources and on average via X-ray stacking) correlated with time since peak in star formation activity?
123.04
Spectral Energy Distribution of Far infrared Detected Quasars in the Lockman Hole
Yu Dai1, J. Huang1, A. Omont2, M. Elvis1, C. Willmer3, E. Hatziminaoglou4, G. Fazio1
1Harvard-Smithsonian Center for Astrophysics, 2Institut d'Astrophysique de Paris, France, 3Steward Observatory, University of Arizona, 4Dept of Astrophysics, Oxford University, United Kingdom.
5:00 PM - 5:10 PM
Staffordshire
The far-infrared (FIR) behavior of quasars is important in disentangling the Starburst (SB) and Active Galactic Nucleus (AGN) contributions to the source. Therefore, we constructed a 24 micron selected Type I quasar sample to study their FIR properties. All of the sources were spectroscopically identified from either the Hectospec on MMT or the Sloan Digital Sky Survey (SDSS). Of the total 432 sources, 37 were detected in the HERMES survey. We compared their SEDs to existing quasar templates, and found that these FIR bright quasars differ only by an additional dust component. Further studies on the origin of the FIR emission reveal the interweaving roles SB and AGN play in powering the dust emission, depending on the dust temperature, luminosities, and the shapes of individual SEDs. The dust temperature has a wide range from 21K to 164K with a median of ~50K, indicating more than one heating mechanism. We argue that the FIR emission and the quasar activities are either serendipitous occurrences or the FIR emission happened in a very short time scale.
123.05
The Quasar SED Mixing Diagram
Heng Hao1, M. Elvis2, F. Civano2
1Harvard Univ., 2SAO.
5:10 PM - 5:20 PM
Staffordshire
We present a useful new diagram for characterizing the quasar-host-reddening mixture for AGN SEDs. This "mixing diagram" is based on a detailed study of 413 X-ray selected Type 1 AGN SEDs from the XMM-COSMOS Survey (Elvis, Hao, et al., 2011). The mixing diagram plots the near-IR (1-3micron) spectral slope against the optical (0.3-1micron) slope to form a generalized 'color-color' diagram. A pure AGN continuum (Elvis et al., 1994, E94) and pure host galaxies are located at clear and distinct positions on the mixing diagram. The lines joining them indicate the fraction of host contribution to each AGN. The reddening vector is almost perpendicular to these mixing lines, and so is easily measured independently.
The mixing diagram shows that ~90% of the AGNs lie on mixing curves between the mean E94 AGN SED and a host galaxy, with only modest reddening [E(B-V)=0.1-0.2] (Hao et al., 2011a). Lower luminosity and lower Eddington ratio AGNs have a larger host galaxy fraction, as expected. Optically selected samples (SDSS) have smaller host galaxy fractions. There is some intrinsic scatter around the E94 mean SED.
A substantial minority, 10%, of the XMM-COSMOS AGNs are inconsistent with any AGN+host+reddening mix. These AGNs have weak or non-existent near-IR bumps, suggesting a lack of the hot dust characteristic of AGNs (Hao et al., 2010). A similar fraction of these "hot dust poor" (HDP) quasars are found in the Elvis et al. 1994 (BQS) and Richards et al. 2006 (SDSS) samples (Hao et al., 2011b). The fraction of "hot dust poor" AGNs grows to ~20% at z>2 (Hao et al. 2010).
The proposed 'cosmic cycle' of SMBH and galaxy co-evolution (e.g. Hopkins et al., 2006) can be shown as tracks on the mixing diagram. The mixing diagram definition could also be expanded to other wavelengths.
123.06
Observed Quasar Structure
Rudolph E. Schild1
1Harvard-Smithsonian, CfA.
5:20 PM - 5:30 PM
Staffordshire
With the introduction of microlensing (nano-lensing) and reverberation analysis, understanding of the luminous structure surrounding quasars has gone from theoretical speculation to an observer's sport. Micro-lensing with day timescale has demonstrated that quasars have structure on scales of 1 R_G which we attribute to the inner edge of the accretion disc, at central distance 70 R_G in lo-hard state (radio loud) Q0957 quasar, indicated by reverberation. Reverberation of the dominant optical continuum has been detected in all 55 hi-soft quasars with brightness data, originating in the dusty torus observed in UV-optical and IR reverberation. Microlensing simulation compared to brightness monitoring shows that 2/3 of the UV-optical continuum originates in the outer torus. The observed color effects observed in the microlensing support the existence of inner and outer luminous structure.
123.07
Lamost Quasar Survey
Xuebing Wu1, LAMOST Extragalactic Survey (LEGAS) Team
1Peking University, China.
5:30 PM - 5:40 PM
Staffordshire
We will introduce the main objectives of the future Chinese LAMOST spectroscopic quasar survey, aiming at discovering 0.4 million new quasars in the next 5 years. This will hopefully provide the largest quasar sample for the further studies of AGNs. The data from the existing and future X-ray surveys will be very helpful in the quasar candidate selection and the constructions of sub-samples of X-ray selected or obscured quasars. We will also describe our improved quasar selection criteria based on the UKIDSS near-IR and SDSS optical colors, and their advantages in recovering the missing quasars in the `redshift desert'. In addition, some recent discoveries of new quasars by the LAMOST commissioning observations will be presented.
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