D. W. Hoard

Eureka Scientific, Oakland, California, United States

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Publications (222)562.66 Total impact

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    ABSTRACT: Novalike cataclysmic variables have persistently high mass transfer rates and prominent steady state accretion disks. We present an analysis of infrared observations of twelve novalikes obtained from the Two Micron All Sky Survey, the Spitzer Space Telescope, and the Wide-field Infrared Survey Explorer All Sky Survey. The presence of an infrared excess at >3-5 microns over the expectation of a theoretical steady state accretion disk is ubiquitous in our sample. The strength of the infrared excess is not correlated with orbital period, but shows a statistically significant correlation (but shallow trend) with system inclination that might be partially (but not completely) linked to the increasing view of the cooler outer accretion disk and disk rim at higher inclinations. We discuss the possible origin of the infrared excess in terms of emission from bremsstrahlung or circumbinary dust, with either mechanism facilitated by the mass outflows (e.g., disk wind/corona, accretion stream overflow, and so on) present in novalikes. Our comparison of the relative advantages and disadvantages of either mechanism for explaining the observations suggests that the situation is rather ambiguous, largely circumstantial, and in need of stricter observational constraints.
    The Astrophysical Journal 03/2014; 786(1). · 6.73 Impact Factor
  • Donald Hoard, Steve Howell, Robert Stencel
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    ABSTRACT: Epsilon Aurigae is the eclipsing binary star with the longest known orbital period, showing a single long (~2 yr) eclipse every 27.1 yr. For the last ~200 years, the nature of the eclipsing object defied explanation. We recently showed that epsilon Aur most likely consists of a high luminosity F0 post-AGB star, and a B5 V star surrounded by a solar system size (~8 AU diameter) disk of dusty material. We propose to continue our IRAC monitoring of epsilon Aur, to characterize the disk's azimuthal thermal variation as its irradiated, warm (1150 K) portion increasingly comes into view. We request 0.2 hr to obtain 2 IRAC observations. If Cycle 10 is extended through Jan 2015, we request another 6 visits (0.6 hr) in Dec 2014, coinciding with the predicted start of coherent pulsations of the F star, which occur every ~3000 days. The most recent eclipse was in Aug 2009-Jul 2011; we are now in the post-eclipse phase, when the heated side of the disk begins rotating into view. During the majority of our past IRAC observations (starting a few months prior to the eclipse ingress), only the cool (550 K) side of the disk was visible. In 2014-2015, as we move toward quadrature, the effect of heating due to the F star will increase the IRAC ch1/ch2 flux ratio. The eclipse of epsilon Aur is a rare event and a unique astrophysical opportunity, since backlighting of the disk by the luminous eclipsed star reveals details that cannot be detected in similar disks around single stars. This is one of the very few astrophysical disks where azimuthal thermal gradients can be mapped and interpreted. Observations of the warm side of the disk are crucial to test and constrain new models of disk structure. As part of our overall monitoring campaign with Spitzer, Hubble, Herschel, and numerous ground-based facilities, the proposed observations will make an important contribution to the understanding of binary stars, including mass transfer and evolution, along with new insights into astrophysical disks and post-AGB star evolution.
    Spitzer Proposal. 10/2013;
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    ABSTRACT: We have compiled photometric data from the Wide-field Infrared Survey Explorer All Sky Survey and other archival sources for the more than 2200 objects in the original McCook & Sion Catalog of Spectroscopically Identified White Dwarfs. We applied color-selection criteria to identify 28 targets whose infrared spectral energy distributions depart from the expectation for the white dwarf photosphere alone. Seven of these are previously known white dwarfs with circumstellar dust disks, five are known central stars of planetary nebulae, and six were excluded for being known binaries or having possible contamination of their infrared photometry. We fit white dwarf models to the spectral energy distributions of the remaining ten targets, and find seven new candidates with infrared excess suggesting the presence of a circumstellar dust disk. We compare the model dust disk properties for these new candidates with a comprehensive compilation of previously published parameters for known white dwarfs with dust disks. It is possible that the current census of white dwarfs with dust disks that produce an excess detectable at K-band and shorter wavelengths is close to complete for the entire sample of known WDs to the detection limits of existing near-IR all-sky surveys. The white dwarf dust disk candidates now being found using longer wavelength infrared data are drawn from a previously underrepresented region of parameter space, in which the dust disks are overall cooler, narrower in radial extent, and/or contain fewer emitting grains.
    The Astrophysical Journal 04/2013; 770(1). · 6.73 Impact Factor
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    ABSTRACT: The WISE Infra-Red Excesses around Degenerates (WIRED) Survey combines WISE photometry of white dwarfs with optical and NIR photometry to carefully search for infrared excesses due to dust and substellar companions in an effort to create a statistical sample of both classes of objects. To date, WIRED has discovered dozens of candidates. In this talk we present an overview of some of these results and follow-up from WIRED, including new results from targets in the McCook & Sion White Dwarf catalog. This work is based on data from: WISE, a joint project of UCLA and JPL/Caltech, funded by NASA; the UKIRT Infrared Deep Sky Survey; the Two Micron All Sky Survey, a joint project of the University of Massachusetts and IPAC/Caltech, funded by NASA and the NSF; the Sloan Digital Sky Survey, and the AAVSO Photometric All-Sky Survey.
    01/2013;
  • Donald Hoard, Steve Howell
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    ABSTRACT: KIC 9535405 is a white dwarf identified as a blue variable object in the Burrell Optical Kepler Survey. Our time-resolved optical spectra of KIC 9535405 show accreted metals in its photosphere, indicating ongoing accretion from a previously undetected circumstellar dust disk (KIC 9535405 is too faint to have been detected by both 2MASS and WISE). Our Kepler time series observations have revealed a photometric period of 6.138 hr. The variability is non-sinusoidal and we have modelled it as due to a cooler (30,000 K) region on the hot (34,000 K) WD photosphere. This cool spot likely maps the zone of accreting metals on the WD surface. We propose here to (1) obtain precise IRAC ch 1 and ch 2 flux density measurements in order to characterize the IR excess due to circumstellar dust, and (2) obtain IRAC ch 1 and ch 2 light curves for comparison with the extant and ongoing Kepler and ground-based monitoring. Despite the causal connection between the presence of a dust disk and metal enrichment of the WD, little is known about the actual mechanism through which matter transits from the dust disk to the WD surface. In that regard, KIC 9535405 is a unique target that can address this gap in our understanding. It is the first dusty WD for which observational information at optical wavelengths shows the non-uniform geographic distribution of accreted material over the surface of the WD, providing an invaluable look at the intermediate steps of the process that starts with the IR excess observational signature of a dusty disk around a WD and ends with the observational signature of metal-enrichment in the optical-UV spectrum of the WD.
    Spitzer Proposal. 12/2012;
  • Donald Hoard, Robert Stencel, Steve Howell
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    ABSTRACT: We request a small investment of 24 minutes of Spitzer time, to obtain four IRAC observations of epsilon Aurigae. A naked eye object located near Capella, epsilon Aurigae is the eclipsing binary star with the longest known orbital period, showing a single long duration (~2 yr) eclipse every 27.1 yr. For much of the last 200 years, the nature of the eclipsing object defied explanation. We recently demonstrated that epsilon Aurigae consists of a high luminosity F0 post-AGB star in orbit with a B5 V star surrounded by a solar system sized (~8 AU diameter) disk of cool, dust-dominated material. The eclipse of epsilon Aurigae is a rare event; moreover, it is a unique astrophysical opportunity, since the backlighting of the disk by the high luminosity eclipsed star reveals details that cannot be detected in similar dusty disks around single stars. The current eclipse started in August 2009 and ended in July 2011; we are now in the post-eclipse phase, when the irradiation-heated side of the disk will begin rotating into view. The goals for these observations include: (1) extend our ongoing IRAC monitoring campaign covering the current eclipse to post-eclipse visits; (2) provide a consistent, well-calibrated space-based set of IR photometry for comparison with ongoing ground-based work; and (3) use the composite results to constrain the thermal profile of the disk. A key expectation of these particular observations is to reveal the irradiation-heated portion of the disk, which will be visible on its trailing side following eclipse. Observations of this side of the disk will be crucial to test and constrain new models of disk structure. As part of our overall monitoring campaign with Spitzer, Hubble, Herschel, and numerous ground-based facilities, these proposed observations will make an important contribution to the understanding of stellar evolution in binary stars, including mass transfer and evolution studies, along with new insights into astrophysical disks and post-AGB star evolution.
    Spitzer Proposal. 12/2012;
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    ABSTRACT: We present the discovery with WISE of a significant infrared excess associated with the eclipsing post-common envelope binary SDSSJ 030308.35+005443.7, the first excess discovered around a non-interacting white dwarf+main sequence M dwarf binary. The spectral energy distribution of the white dwarf+M dwarf companion shows significant excess longwards of 3-microns. A T_eff of 8940K for the white dwarf is consistent with a cooling age >2 Gyr, implying that the excess may be due to a recently formed circumbinary dust disk of material that extends from the tidal truncation radius of the binary at 1.96 Rsun out to <0.8 AU, with a total mass of ~10^20 g. We also construct WISE and follow-up ground-based near-infrared light curves of the system, and find variability in the K-band that appears to be in phase with ellipsoidal variations observed in the visible. The presence of dust might be due to a) material being generated by the destruction of small rocky bodies that are being perturbed by an unseen planetary system or b) dust condensing from the companion's wind. The high inclination of this system, and the presence of dust, make it an attractive target for M dwarf transit surveys and long term photometric monitoring.
    The Astrophysical Journal 09/2012; 759(1). · 6.73 Impact Factor
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    ABSTRACT: We report observations of a possible young transiting planet orbiting a previously known weak-lined T-Tauri star in the 7-10 Myr old Orion-OB1a/25-Ori region. The candidate was found as part of the Palomar Transient Factory (PTF) Orion project. It has a photometric transit period of 0.448413 +- 0.000040 days, and appears in both 2009 and 2010 PTF data. Follow-up low-precision radial velocity (RV) observations and adaptive optics imaging suggest that the star is not an eclipsing binary, and that it is unlikely that a background source is blended with the target and mimicking the observed transit. RV observations with the Hobby-Eberly and Keck telescopes yield an RV that has the same period as the photometric event, but is offset in phase from the transit center by approximately -0.22 periods. The amplitude (half range) of the RV variations is 2.4 km/s and is comparable with the expected RV amplitude that stellar spots could induce. The RV curve is likely dominated by stellar spot modulation and provides an upper limit to the projected companion mass of M_p sin i_orb < 4.8 +- 1.2 M_Jup; when combined with the orbital inclination, i orb, of the candidate planet from modeling of the transit light curve, we find an upper limit on the mass of the planetary candidate of M_p < 5.5 +- 1.4 M_Jup. This limit implies that the planet is orbiting close to, if not inside, its Roche limiting orbital radius, so that it may be undergoing active mass loss and evaporation.
    The Astrophysical Journal 06/2012; 755(1). · 6.73 Impact Factor
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    ABSTRACT: We present Herschel Space Observatory photometric observations of the unique, long-period eclipsing binary star Epsilon Aurigae. Its extended spectral energy distribution is consistent with our previously published cool (550 K) dust disk model. We also present an archival infrared spectral energy distribution of the side of the disk facing the bright F-type star in the binary, which is consistent with a warmer (1150 K) disk model. The lack of strong molecular emission features in the Herschel bands suggests that the disk has a low gas-to-dust ratio. The spectral energy distribution and Herschel images imply that the 250 GHz radio detection reported by Altenhoff et al. is likely contaminated by infrared-bright, extended background emission associated with a nearby nebular region and should be considered an upper limit to the true flux density of Epsilon Aur.
    The Astrophysical Journal Letters 02/2012; 748(2). · 6.35 Impact Factor
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    ABSTRACT: Spitzer IRAC observations of 15 metal-polluted white dwarfs reveal infrared excesses in the spectral energy distributions of HE 0110-5630, GD 61, and HE 1349-2305. All three of these stars have helium-dominated atmospheres, and their infrared emissions are consistent with warm dust produced by the tidal destruction of (minor) planetary bodies. This study brings the number of metal-polluted, helium and hydrogen atmosphere white dwarfs surveyed with IRAC to 53 and 38 respectively. It also nearly doubles the number of metal-polluted helium-rich white dwarfs found to have closely orbiting dust by Spitzer. From the increased statistics for both atmospheric types with circumstellar dust, we derive a typical disk lifetime of log[t_{disk} (yr)] = 5.6+-1.1 (ranging from 3*10^4 - 5*10^6 yr). This assumes a relatively constant rate of accretion over the timescale where dust persists, which is uncertain. We find that the fraction of highly metal-polluted helium-rich white dwarfs that have an infrared excess detected by Spitzer is only 23 per cent, compared to 48 per cent for metal-polluted hydrogen-rich white dwarfs, and we conclude from this difference that the typical lifetime of dusty disks is somewhat shorter than the diffusion time scales of helium-rich white dwarf. We also find evidence for higher time-averaged accretion rates onto helium-rich stars compared to the instantaneous accretion rates onto hydrogen-rich stars; this is an indication that our picture of evolved star-planetary system interactions is incomplete. We discuss some speculative scenarios that can explain the observations.
    The Astrophysical Journal 02/2012; 749(2). · 6.73 Impact Factor
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    ABSTRACT: The Spitzer Science Center and NASA Infrared Science Archive (IRSA) will produce and release a set of Enhanced Imaging Products from the Spitzer Heritage Archive. We anticipate a preliminary release of a subset of the data in time for the January 2012 AAS. A release of the full set of products for the Spitzer cryogenic mission will fall in mid-to-late 2012. These products will include enhanced mosaics created using data from multiple programs where appropriate and a source list (SL) of photometry for compact sources. The primary requirement on the SL is very high reliability -- with areal coverage, completeness and limiting depth being secondary considerations. The enhanced imaging products will include data from the four channels of IRAC (3-8 microns) and the 24 micron channel of MIPS. The products will be generated for Spitzer observations of about 1500 square degrees and include around 30 million sources.
    01/2012;
  • D. W. Hoard
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    ABSTRACT: Recent infrared observations, particularly from the Spitzer Space Telescope, of white dwarfs, cataclysmic variables and other interacting compact binaries, have revealed the presence of dust in many systems. I review the discovery, properties, and implications of dust around white dwarfs and cataclysmic variables.
    Memorie della Societa Astronomica Italiana. 01/2012;
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    ABSTRACT: The Wide-field Infrared Survey Explorer (WISE) is a NASA medium class Explorer mission that was launched on 2009 December 14. WISE mapped the entire sky simultaneously in four infrared (IR) bands centered at 3.4, 4.6, 12, and 22um (denoted W1, W2, W3, and W4, respectively). The WISE InfraRed Excesses around Degenerates (WIRED) Survey is designed to detect IR excesses around white dwarfs (WDs) using photometry from the WISE catalog. In this paper, we focus on the WISE detections of SDSS DR7 WDs (Kleinman, S.J. 2010AIPC.1273..156K), which we examined as part of the WIRED Survey. (7 data files).
    VizieR Online Data Catalog. 01/2012;
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    ABSTRACT: With the launch of the {\em Wide-field Infrared Survey Explorer} ({\em WISE}), a new era of detecting planetary debris and brown dwarfs around white dwarfs (WDs) has begun with the {\em WISE} InfraRed Excesses around Degenerates (WIRED) Survey. The WIRED Survey is sensitive to substellar objects and dusty debris around WDs out to distances exceeding 100 pc, well beyond the completeness level of local WDs. In this paper, we present a cross-correlation of the preliminary Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) WD Catalog between the {\em WISE}, Two-Micron All Sky Survey (2MASS), UKIRT Infrared Deep Sky Survey (UKIDSS), and SDSS DR7 photometric catalogs. From $\sim18,000$ input targets, there are {\em WISE} detections comprising 344 "naked" WDs (detection of the WD photosphere only), 1020 candidate WD+M dwarf binaries, 42 candidate WD+brown dwarf (BD) systems, 52 candidate WD+dust disk systems, and 69 targets with indeterminate infrared excess. We classified all of the detected targets through spectral energy distribution model fitting of the merged optical, near-IR, and {\em WISE} photometry. Some of these detections could be the result of contaminating sources within the large ($\approx6\arcsec$) {\em WISE} point spread function; we make a preliminary estimate for the rates of contamination for our WD+BD and WD+disk candidates, and provide notes for each target-of-interest. Each candidate presented here should be confirmed with higher angular resolution infrared imaging or infrared spectroscopy. We also present an overview of the observational characteristics of the detected WDs in the {\em WISE} photometric bands, including the relative frequencies of candidate WD+M, WD+BD, and WD+disk systems.
    The Astrophysical Journal Supplement Series 10/2011; 197(2). · 16.24 Impact Factor
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    ABSTRACT: We report here on a series of medium resolution spectro-photometric observations of the enigmatic long period eclipsing binary epsilon Aurigae, during its eclipse interval of 2009-2011, using near-infrared spectra obtained with SpeX on the Infrared Telescope Facility (IRTF), mid-infrared spectra obtained with BASS on AOES and IRTF, MIRSI on IRTF, and MIRAC4 on the MMT, along with mid-infrared photometry using MIRSI on IRTF and MIRAC4 on the MMT, plus 1995-2000 timeframe published photometry and data obtained with Denver's TNTCAM2 at WIRO. The goals of these observations included: (1) comparing eclipse depths with prior eclipse data, (2) confirming the re-appearance of CO absorption bands at and after mid-eclipse, associated with sublimation in the disk, (3) seeking evidence for any mid-infrared solid state spectral features from particles in the disk, and (4) providing evidence that the externally irradiated disk has azimuthal temperature differences. IR eclipse depths appear similar to those observed during the most recent (1983) eclipse, although evidence for post-mid-eclipse disk temperature increase is present, due to F star heated portions of the disk coming into view. Molecular CO absorption returned 57 days after nominal mid-eclipse, but was not detected at mid-eclipse plus 34 days, narrowing the association with differentially heated sub-regions in the disk. Transient He I 10830A absorption was detected at mid-eclipse, persisting for at least 90 days thereafter, providing a diagnostic for the hot central region. The lack of solid-state features in Spitzer Infrared Spectrograph, BASS, and MIRAC spectra to date suggests the dominance of large particles (micron-sized) in the disk. Based on these observations, mid-infrared studies out of eclipse can directly monitor and map the disk thermal changes, and better constrain disk opacity and thermal conductivity.
    The Astronomical Journal 10/2011; 142(5):174. · 4.97 Impact Factor
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    ABSTRACT: The Palomar Transient Factory (PTF) Orion project is one of the experiments within the broader PTF survey, a systematic automated exploration of the sky for optical transients. Taking advantage of the wide (35 × 23) field of view available using the PTF camera installed at the Palomar 48 inch telescope, 40 nights were dedicated in 2009 December to 2010 January to perform continuous high-cadence differential photometry on a single field containing the young (7-10 Myr) 25 Ori association. Little is known empirically about the formation of planets at these young ages, and the primary motivation for the project is to search for planets around young stars in this region. The unique data set also provides for much ancillary science. In this first paper, we describe the survey and the data reduction pipeline, and present some initial results from an inspection of the most clearly varying stars relating to two of the ancillary science objectives: detection of eclipsing binaries and young stellar objects. We find 82 new eclipsing binary systems, 9 of which are good candidate 25 Ori or Orion OB1a association members. Of these, two are potential young W UMa type systems. We report on the possible low-mass (M-dwarf primary) eclipsing systems in the sample, which include six of the candidate young systems. Forty-five of the binary systems are close (mainly contact) systems, and one of these shows an orbital period among the shortest known for W UMa binaries, at 0.2156509 ± 0.0000071 days, with flat-bottomed primary eclipses, and a derived distance that appears consistent with membership in the general Orion association. One of the candidate young systems presents an unusual light curve, perhaps representing a semi-detached binary system with an inflated low-mass primary or a star with a warped disk, and may represent an additional young Orion member. Finally, we identify 14 probable new classical T-Tauri stars in our data, along with one previously known (CVSO 35) and one previously reported as a candidate weak-line T-Tauri star (SDSS J052700.12+010136.8).
    The Astronomical Journal 07/2011; 142(2):60. · 4.97 Impact Factor
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    ABSTRACT: We propose a uniform survey of 37 nearby pulsars in order to determine the overall frequency of debris disks around neutron stars. Debris disks around neutron stars are invoked in the formation mechanism of the planets around the pulsar PSR 1257+12 and to explain the intermittent cessation of pulsations for a substantial number of radio pulsars. Furthermore, simulations of supernova explosions predict the existence of so-called fallback disks of material that is not ejected during the supernova. However, the direct detection of such disks has proven elusive. We currently only know of two examples, both discovered with Spitzer around isolated X-ray pulsars. This lack of disk detections might simply be a consequence of the limited size and depth of the observed sample. The presence of such disks has important implications for the general properties of the neutron star population, affecting the spin-down evolution and distribution of magnetic field strength and ages. Additional observations are needed to evaluate whether debris disks are a common feature in the evolution of neutron stars.
    Spitzer Proposal. 05/2011;
  • Donald Hoard, R. Stencel, S. Howell
    [Show abstract] [Hide abstract]
    ABSTRACT: We request a small investment of 24 minutes of Spitzer time, to obtain four IRAC observations of epsilon Aurigae. A naked eye object located near Capella, epsilon Aurigae is the eclipsing binary star with the longest known orbital period, showing a single long duration (~2 yr) eclipse every 27.1 yr. For much of the last 150 years, the nature of the eclipsing object defied explanation. We recently demonstrated that epsilon Aurigae consists of a high luminosity F0 post-AGB star in orbit with a B5 V star surrounded by a solar system sized (~8 AU diameter) disk of cool, dust-dominated material. The eclipse of epsilon Aurigae is a rare event; moreover, it is a unique astrophysical opportunity, since the backlighting of the disk by the high luminosity eclipsed star reveals details that cannot be detected in similar dusty disks around single stars. The current eclipse started in August 2009 and is expected to reach its photometric conclusion in May 2011 (with the spectroscopic conclusion as late as December 2011). The goals for these observations include: (1) extend our ongoing IRAC monitoring campaign covering the current eclipse to late-phase and post-eclipse visits; (2) provide a consistent, well-calibrated space-based set of IR photometry for comparison with ongoing ground-based work; and (3) use the composite results to constrain the thermal profile of the disk. A key expectation of these particular observations is to reveal the irradiation-heated portion of the disk, which will be visible on its trailing side following eclipse. Observations of this side of the disk will be crucial to test and constrain new models of disk structure. As part of our overall monitoring campaign with Spitzer, Hubble, Herschel, and numerous ground-based facilities, these proposed observations will make an important contribution to the understanding of stellar evolution in binary stars, including mass transfer and evolution studies, along with new insights into astrophysical disks and post-AGB star evolution.
    Spitzer Proposal. 05/2011;
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    ABSTRACT: We present the results of a deep, wide-field CCD survey for the open cluster NGC~3532. Our new $BV(RI)_{c}$ photometry effectively covers a one square degree area and reaches an unprecedented depth of $V\sim21$ to reveal that NGC~3532 is a rich open cluster that harbors a large number of faint, low-mass stars. We employ a number of methods to reduce the impact of field star contamination in the cluster color-magnitude diagrams, including supplementing our photometry with $JHK_{s}$ data from the 2MASS catalog. These efforts allow us to define a robust sample of candidate main sequence stars suitable for a purely empirical determination of the cluster's parameters by comparing them to the well-established Hyades main sequence. Our results confirm previous findings that NGC~3532 lies fairly near to the Sun [$(m-M)_0=8.46\pm0.05$; $492^{+12}_{-11}$~pc] and has an extremely low reddening for its location near the Galactic plane [$E(B-V)=0.028\pm0.006$]. Moreover, an age of $\sim300$\,Myr has been derived for the cluster by fitting a set of overshooting isochrones to the well-populated upper main-sequence. This new photometry also extends faint enough to reach the cluster white dwarf sequence, as confirmed by our photometric recovery of eight spectroscopically identified members of the cluster. Using the location of these eight members, along with the latest theoretical cooling tracks, we have identified $\sim30$ additional white dwarf stars in the $[V,~(B-V)]$ color-magnitude diagram that have a high probability of belonging to NGC~3532. The age we derive from fitting white dwarf isochrones to the locus of these stars, $300\pm100$\,Myr, is consistent with the age derived from the turnoff. Our analysis of the photometry also includes an estimation of the binary star fraction, as well as a determination of the cluster's luminosity and mass functions.
    The Astronomical Journal 01/2011; · 4.97 Impact Factor
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    ABSTRACT: We report on our ongoing efforts to characterize the luminous central stars of circumstellar shell sources discovered with the Spitzer Space Telescope. The objects in our selection are highly symmetric, circular and elliptical shells, most prominent at 24mum, and the vast majority of the shells and central sources has never been studied previously. We obtained near-IR spectroscopic observations of the central stars and find the overwhelming number of these objects to be massive stars, including new Wolf Rayet stars and Luminous Blue Variable candidates.
    01/2011;

Publication Stats

657 Citations
562.66 Total Impact Points

Institutions

  • 2014
    • Eureka Scientific
      Oakland, California, United States
  • 2013
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 2003–2012
    • California Institute of Technology
      • Spitzer Science Center
      Pasadena, California, United States
  • 2010
    • Indiana University Bloomington
      • Department of Astronomy
      Bloomington, Indiana, United States
  • 1998–2009
    • University of Washington Seattle
      • Department of Astronomy
      Seattle, WA, United States
  • 2007
    • University of Leicester
      • Department of Physics and Astronomy
      Leiscester, England, United Kingdom
  • 2005
    • Harvey Mudd College
      • Physics
      Tucson, AZ, United States
  • 2004
    • Gemini Observatory
      Hilo, Hawaii, United States
  • 2001
    • National Optical Astronomy Observatory
      Tucson, Arizona, United States
  • 1999
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States