Search

This letter reports 12 novel spectroscopic detections of warm circumstellar dust orbiting polluted white dwarfs using JWST MIRI. The disks span two orders of magnitude in fractional infrared brightness and more than double the number of white dwarf dust spectra available for mineralogical study. Among the highlights are: i) the two most subtle infrared excesses yet detected, ii) the strongest silicate emission features known for any debris disk orbiting any main-sequence or white dwarf star, iii) one disk with a thermal continuum but no silicate emission, and iv) three sources with likely spectral signatures of silica glass. The near ubiquity of solid-state emission requires small dust grains that are optically thin, and thus must be replenished on year-to-decade timescales by ongoing collisions. The disk exhibiting a featureless continuum can only be fit by dust temperatures in excess of 2000K, implying highly refractory material comprised of large particles, or non-silicate mineral species. If confirmed, the glassy silica orbiting three stars could be indicative of high-temperature processes and subsequent rapid cooling, such as occur in high-velocity impacts or vulcanism. These detections have been enabled by the unprecedented sensitivity of MIRI LRS spectroscopy and highlight the capability and potential for further observations in future cycles., Comment: Accepted to ApJ Letters, 10 pages, 3 figures, 1 table

We report the discovery of the youngest brown dwarf with a disk at 102 pc from the Sun, WISEA~J120037.79-784508.3 (W1200-7845), via the Disk Detective citizen science project. We establish that W1200-7845 is located in the 3.7$\substack{+4.6 \\ -1.4}$ Myr-old $\varepsilon$~Cha association. Its spectral energy distribution (SED) exhibits clear evidence of an infrared (IR) excess, indicative of the presence of a warm circumstellar disk. Modeling this warm disk, we find the data are best fit using a power-law description with a slope $\alpha = -0.94$, which suggests it is a young, Class II type disk. Using a single blackbody disk fit, we find $T_{eff, disk} = 521 K$ and $L_{IR}/L_{*} = 0.14$. The near-infrared spectrum of W1200-7845 matches a spectral type of M6.0$\gamma \pm 0.5$, which corresponds to a low surface gravity object, and lacks distinctive signatures of strong Pa$\beta$ or Br$\gamma$ accretion. Both our SED fitting and spectral analysis indicate the source is cool ($T_{eff} = $2784-2850 K), with a mass of 42-58 $M_{Jup}$, well within the brown dwarf regime. The proximity of this young brown dwarf disk makes the system an ideal benchmark for investigating the formation and early evolution of brown dwarfs.

We present the discovery and asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494-7018 (TIC 278659026), monitored in TESS first sector using 120-second cadence. The light curve analysis reveals that EC 21494-7018 is a sdB pulsator counting up to 20 frequencies associated with independent g-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from Gaia DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 +/- 0.009 Msun) is significantly lower than the typical mass of sdB stars, and suggests that its progenitor has not undergone the He-core flash, and therefore could originate from a massive (>2 Msun) red giant, an alternative channel for the formation of hot B subdwarfs. Other derived parameters include the H-rich envelope mass (0.0037 +/- 0.0010 Msun), radius (0.1694 +/- 0.0081 Rsun), and luminosity (8.2+/-1.1 Lsun). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494-7018 has burnt ~43% (in mass) of its central helium and possesses a relatively large mixed core (Mcore = 0.198 +/- 0.010 Msun), in line with trends already uncovered from other g-mode sdB pulsators analysed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass; X(O)core = 0.16 -0.05 +0.13) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain C12(alpha,gamma)O16 nuclear reaction rate., Comment: Published in A&A

The Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) contains the only currently operating coronagraph in space that is not trained on the Sun. In an era of extreme--adaptive-optics--fed coronagraphs, and with the possibility of future space-based coronagraphs, we re-evaluate the contrast performance of the STIS CCD camera. The 50CORON aperture consists of a series of occulting wedges and bars, including the recently commissioned BAR5 occulter. We discuss the latest procedures in obtaining high contrast imaging of circumstellar disks and faint point sources with STIS. For the first time, we develop a noise model for the coronagraph, including systematic noise due to speckles, which can be used to predict the performance of future coronagraphic observations. Further, we present results from a recent calibration program that demonstrates better than $10^{-6}$ point-source contrast at 0.6", ranging to $3\times10^{-5}$ point-source contrast at 0.25". These results are obtained by a combination of sub-pixel grid dithers, multiple spacecraft orientations, and post-processing techniques. Some of these same techniques will be employed by future space-based coronagraphic missions. We discuss the unique aspects of STIS coronagraphy relative to ground-based adaptive-optics--fed coronagraphs., Comment: 61 pages, 12 figures, accepted to JATIS

The infrared dust emission from the white dwarf GD 56 is found to rise and fall by 20% peak-to-peak over 11.2 yr, and is consistent with ongoing dust production and depletion. It is hypothesized that the dust is produced via collisions associated with an evolving dust disk, temporarily increasing the emitting surface of warm debris, and is subsequently destroyed or assimilated within a few years. The variations are consistent with debris that does not change temperature, indicating that dust is produced and depleted within a fixed range of orbital radii. Gas produced in collisions may rapidly re-condense onto grains, or may accrete onto the white dwarf surface on viscous timescales that are considerably longer than Poynting-Robertson drag for micron-sized dust. This potential delay in mass accretion rate change is consistent with multi-epoch spectra of the unchanging Ca II and Mg II absorption features in GD 56 over 15 yr, although the sampling is sparse. Overall these results indicate that collisions are likely to be the source of dust and gas, either inferred or observed, orbiting most or all polluted white dwarfs., Comment: 11 pages, 6 figures, and 2 tables. Accepted to MNRAS

We present the first scattered-light images of two debris disks around the F8 star HD 104860 and the F0V star HD 192758, respectively $\sim45$ and $\sim67$ pc away. We detected these systems in the F110W and F160W filters through our re-analysis of archival Hubble Space Telescope NICMOS data with modern starlight subtraction techniques. Our image of HD 104860 confirms the morphology previously observed by Herschel in thermal emission with a well-defined ring at radius $\sim114$ au inclined $\sim58$ degrees. Although the outer edge profile is consistent with dynamical evolution models, the sharp inner edge suggests sculpting by unseen perturbers. Our images of HD 192758 reveal a disk at radius $\sim95$ au inclined by $\sim59$ degrees, never resolved so far. These disks have low scattering albedos of 10% and 13% respectively, inconsistent with water ice grain compositions. They are reminiscent of several other disks with similar inclination and scattering albedos: Fomalhaut, HD 92945, HD 202628, and HD 207129. They are also very distinct from brighter disks in the same inclination bin, which point to different compositions between these two populations. Varying scattering albedo values can be explained by different grain porosities, chemical compositions, or grain size distributions, which may indicate distinct formation mechanisms or dynamical processes at work in these systems. Finally, these faint disks with large infrared excesses may be representative of an underlying population of systems with low albedo values. Searches with more sensitive instruments on HST or on the James Webb Space Telescope and using state-of-the art starlight-subtraction methods may help discover more of such faint systems., Comment: Accepted for publication in ApJ

We present the first scattered-light images of the debris disk around 49 ceti, a ~40 Myr A1 main sequence star at 59 pc, famous for hosting two massive dust belts as well as large quantities of atomic and molecular gas. The outer disk is revealed in reprocessed archival Hubble Space Telescope NICMOS F110W images, as well as new coronagraphic H band images from the Very Large Telescope SPHERE instrument. The disk extends from 1.1" (65 AU) to 4.6" (250 AU), and is seen at an inclination of 73degr, which refines previous measurements at lower angular resolution. We also report no companion detection larger than 3 M_Jup at projected separations beyond 20 AU from the star (0.34"). Comparison between the F110W and H-band images is consistent with a grey color of 49 ceti's dust, indicating grains larger than >2microns. Our photometric measurements indicate a scattering efficiency / infrared excess ratio of 0.2-0.4, relatively low compared to other characterized debris disks. We find that 49 ceti presents morphological and scattering properties very similar to the gas-rich HD 131835 system. From our constraint on the disk inclination we find that the atomic gas previously detected in absorption must extend to the inner disk, and that the latter must be depleted of CO gas. Building on previous studies, we propose a schematic view of the system describing the dust and gas structure around 49 ceti and hypothetic scenarios for the gas nature and origin., Comment: Accepted for publication in ApJL. 7 pages, 4 figures

The search for transiting habitable exoplanets has broadened to include several types of stars that are smaller than the Sun in an attempt to increase the observed transit depth and hence the atmospheric signal of the planet. Of all spectral types, white dwarfs are the most favorable for this type of investigation. The fraction of white dwarfs that possess close-in rocky planets is unknown, but several large angle stellar surveys have the photometric precision and cadence to discover at least one if they are common. Ultraviolet observations of white dwarfs may allow for detection of molecular oxygen or ozone in the atmosphere of a terrestrial planet. We use archival Hubble Space Telescope data from the Cosmic Origins Spectrograph to search for transiting rocky planets around UV-bright white dwarfs. In the process, we discovered unusual variability in the pulsating white dwarf GD 133, which shows slow sinusoidal variations in the UV. While we detect no planets around our small sample of targets, we do place stringent limits on the possibility of transiting planets, down to sub-lunar radii. We also point out that non-transiting small planets in thermal equilibrium are detectable around hotter white dwarfs through infrared excesses, and identify two candidates., Comment: 42 pages, 17 figures, accepted to ApJ

We observe a significant change in the TW Hya disk interior to 40~AU via archival unpolarized multi-wavelength Hubble Space Telescope/STIS and NICMOS images with an inner working angle (IWA) of 0\farcs4 (22~AU). Our images show the outer edge of a clearing at every wavelength with similar behavior, demonstrating that the feature is structural, rather than due to some property of polarized light in the disk. We compare our observations to those taken by Akiyama et al. (2015) and Rapson et al. (2015), and discuss the spectral evolution of the disk interior to 80~AU. We construct a model with two gaps: one at 30~AU and one at 80~AU that fit the observed surface brightness profile but overpredicts the absolute brightness of the disk. Our models require an additional dimming to be consistent with observations, which we tentatively ascribe to shadowing. The gap structures seen in scattered light are spatially coincident with sub-mm detections of CO and N$_2$H$^+$, and are near expected condensation fronts of these molecular species, providing tentative evidence that the structures seen in scattered light may be correlated with chemical changes in the disk., Comment: 13 pages, 3 figures, accepted to ApJ Letters

We present a 0.5-2.2 micron scattered light spectrum of the circumstellar disk around TW Hya from a combination of spatially resolved HST STIS spectroscopy and NICMOS coronagraphic images of the disk. We investigate the morphology of the disk at distances > 40 AU over this wide range of wavelengths, and identify the presence of a depression in surface brightness at ~80 AU that could be caused by a gap in the disk. Additionally, we quantify the surface brightness, azimuthal symmetry, and spectral character of the disk as a function of radius. Our analysis shows that the scattering efficiency of the dust is largely neutral to blue over the observed wavelengths. We model the disk as a steady alpha-disk with an ad hoc gap structure. The thermal properties of the disk are self-consistently calculated using a three-dimensional radiative transfer code that uses ray-tracing to model the heating of the disk interior and scattered light images. We find a good fit to the data over a wide range of distances from the star if we use a model disk with a partially filled gap of 30% depth at 80 AU and with a self-similar truncation knee at 100 AU. The origin of the gap is unclear, but it could arise from a transition in the nature of the disk's dust composition or the presence of a planetary companion. Based on scalings to previous hydrodynamic simulations of gap opening criteria for embedded proto-planets, we estimate that a planetary companion forming the gap could have a mass between 6-28 M_Earth., Comment: To appear in ApJ online on June 14; 43 pages, 14 figures

Single metal polluted white dwarfs with no dusty disks are believed to be actively accreting metals from a circumstellar disk of gas caused by the destruction of asteroids perturbed by planetary systems. We report, for the first time, the detection of circumstellar Ca~II gas in absorption around the DAZ WD~1124-293, which lacks an infrared excess. We constrain the gas to $>$7 $R_{\rm WD}$ and $<$32000~AU, and estimate it to be at $\sim$54~R$_{\rm WD}$, well within WD~1124-293's tidal disruption radius. This detection is based on several epochs of spectroscopy around the Ca~II H and K lines ($\lambda$=3968\AA, 3933\AA) with the MIKE spectrograph on the Magellan/Clay Telescope at Las Campanas Observatory. We confirm the circumstellar nature of the gas by observing nearby sightlines and finding no evidence for gas from the local interstellar medium. Through archival data we have measured the equivalent width of the two photospheric Ca lines over a period of 11 years. We see $<$ 5-7\% epoch-to-epoch variation in equivalent widths over this time period, and no evidence for long term trends. The presence of a circumstellar gas implies a near edge-on inclination to the system, thus we place limits to short period transiting planetary companions with R $>$ R$_{\rm \oplus}$ using the WASP survey. The presence of gas in orbit around WD~1124-293 implies that most DAZs could harbor planetary systems. Since 25-30\% of white dwarfs show metal line absorption, the dynamical process for perturbing small bodies must be robust., Comment: 31 pages with 9 figures; accepted to ApJ

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., Comment: 73 pages, 23 figures, Accepted to ApJS. Full tables available at http://www.stsci.edu/~debes/tools.html

With the launch of the Wide-Field Infrared Survey Explorer (WISE), a new era of detecting planetary debris around white dwarfs has begun with the WISE InfraRed Excesses around Degenerates (WIRED) Survey. The WIRED Survey will be sensitive to substellar objects and dusty debris around white dwarfs out to distances exceeding 100 pc, well beyond the completeness level of local WDs and covering a large fraction of known WDs detected with the SDSS DR4 white dwarf catalogue. In this paper we report an initial result of the WIRED survey, the detection of the heavily polluted hydrogen white dwarf (spectral type DAZ) GALEX J193156.8+011745 at 3.35 and 4.6 \micron. We find that the excess is consistent with either a narrow dusty ring with an inner radius of 29 $R_{\rm WD}$, outer radius of 40 $R_{\rm WD}$, and a face-on inclination, or a disk with an inclination of 70$^\circ$, an inner radius of 23 $R_{\rm WD}$, and an outer radius of 80 $R_{\rm WD}$. We also report initial optical spectroscopic monitoring of several metal lines present in the photosphere and find no variability in the line strengths or radial velocities of the lines. We rule out all but planetary mass companions to GALEX1931 out to 0.5 AU., Comment: 19 pages, 3 figures, accepted by ApJ

We detect the HD 32297 debris disk in scattered light at 1.6 and 2.05 \micron. We use these new observations together with a previous scattered light image of the disk at 1.1 \micron to examine the structure and scattering efficiency of the disk as a function of wavelength. In addition to surface brightness asymmetries and a warped morphology beyond $\sim$1\farcs5 for one lobe of the disk, we find that there exists an asymmetry in the spectral features of the grains between the northeastern and southwestern lobes. The mostly neutral color of the disk lobes imply roughly 1 \micron-sized grains are responsible for the scattering. We find that the asymmetries in color and morphology can plausibly be explained by HD 32297's motion into a dense ISM cloud at a relative velocity of 15 km s$^{-1}$. We model the interaction of dust grains with HI gas in the cloud. We argue that supersonic ballistic drag can explain the morphology of the debris disks of HD 32297, HD 15115, and HD 61005., Comment: 14 pages, 7 figures, emulateapj, to appear in Sep 1 ApJ

According to current plans, the SIM/NASA mission will be launched just after the end of operations for the Gaia/ESA mission. This is a new situation which enables long term astrometric projects that could not be achieved by either mission alone. Using the well-known perspective acceleration effect on astrometric measurements, the true heliocentric radial velocity of a nearby star can be measured with great precision if the time baseline of the astrometric measurements is long enough. Since white dwarfs are compact objects, the gravitational redshift can be quite large (40-80 km/s), and is the predominant source of any shift in wavelength. The mismatch of the true radial velocity with the spectroscopic shift thus leads to a direct measure of the Mass--Radius relation for such objects. Using available catalog information about the known nearby white dwarfs, we estimate how many masses/gravitational redshift measurements can be obtained with an accuracy better than 2%. Nearby white dwarfs are relatively faint objects (10 < V < 15), which can be easily observed by both missions. We also briefly discuss how the presence of a long period planet can mask the astrometric signal of perspective acceleration., Comment: 3 pages, 2 Figures. Proceedings of the IAU Symposium 261 : Relativity in Fundamental Astronomy. 27 April - 1 May 2009, Virginia Beach, VA, USA. refereed and accepted version

[abridged] We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC300. We find that the transient (NGC300 OT2008-1) has a peak absolute magnitude of M_bol~-11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km/s) hydrogen Balmer lines and CaII emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect broad CaII H&K absorption with an asymmetric red wing extending to ~1000 km/s, indicative of gas infall onto a massive and relatively compact star (blue supergiant or Wolf-Rayet star); an extended red supergiant progenitor is unlikely. The origin of the inflowing gas may be a previous ejection from the progenitor or the wind of a massive binary companion. The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6x10^4 L_sun, indicative of a ~10-20 M_sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst., Comment: Submitted to ApJ; emulateapj style; 39 pages; 26 figures

We have obtained high spatial resolution imaging observations of the HR 4796A circumstellar debris dust ring using the broad optical response of the Hubble Space Telescope Imaging Spectrograph in coronagraphic mode. We use our visual wavelength observations to improve upon the earlier measured geometrical parameters of the ring-like disk. Two significant flux density asymmetries are noted: (1) preferential forward scattering by the disk grains and (2) an azimuthal surface brightness anisotropy about the morphological minor axis of the disk with corresponding differential ansal brightness. We find the debris ring offset from the location of the star by ~1.4 AU, a shift insufficient to explain the differing brightnesses of the NE and SW ansae simply by the 1/$r^2$ dimmunition of starlight. The STIS data also better quantify the radial confinement of the starlight-scattering circumstellar debris, to a characteristic region <14 AU in photometric half-width, with a significantly steeper inner truncation than outward falloff in radial surface brightness. The inferred spatial distribution of the disk grains is consistent with the possibility of one or more unseen co-orbital planetary-mass perturbers, and the colors of the disk grains are consistent with a collisionally evolved population of debris, possibly including ices reddened by radiation exposure to the central star., Comment: Accepted to AJ; 3 of 8 figures in color

We report HST/NICMOS coronagraphic images of the HD 15115 circumstellar disk at 1.1\micron. We find a similar morphology to that seen in the visible and at H band--an edge-on disk that is asymmetric in surface brightness. Several aspects of the 1.1\micron data are different, highlighting the need for multi-wavelength images of each circumstellar disk. We find a flattening to the western surface brightness profile at 1.1\micron interior to 2\arcsec (90 AU) and a warp in the western half of the disk. We measure the surface brightness profiles of the two disk lobes and create a measure of the dust scattering efficiency between 0.55-1.65\micron at 1\arcsec, 2\arcsec, and 3\arcsec. At 2\arcsec the western lobe has a neutral spectrum up to 1.1\micron and a strong absorption or blue spectrum $>$1.1\micron, while a blue trend is seen in the eastern lobe. At 1\arcsec the disk has a red F110W-H color in both lobes., Comment: 4 pages, 4 figures, emulateapj; accepted to ApJL

The pulsating white dwarf G29-38 possesses a dust disk and metal lines attributed to the accretion of its disk material. \citet{vonhipg29} have reported variability in the equivalent width of G29-38's CaII K line on the timescale of days. We use high resolution optical spectroscopy of G29-38's CaII K line to test this observation. Over six days spanning in June 2007 and October 2007 we see no evidence for variability in the equivalent width of the Ca II K line. We also sample the variability of the Ca II K line over integrated timescales of $\sim$100-500 seconds, where errors from incomplete coverage of pulsation modes are predicted to be $\sim$8-15%. We find that the scatter of the equivalent widths over this time period is consistent with measurement errors at the 7% level, slightly weaker than predicted but within the uncertainties of predictions. Weaker Ca and Mg lines observed show no significant variability on yearly timescales over ten years based on our data and other high resolution spectra. We conclude that further study is warranted to verify if the accretion onto G29-38 is variable., Comment: 14 pages, 4 figures, Accepted to ApJL

We combine HST/NICMOS imaging photometry of the HR 4796A disk at previously unobserved wavelengths between 1.71-2.22\micron with reprocessed archival observations to produce a measure of the dust's scattering efficiency as a function of wavelength. The spectrum of the dust, synthesized from the seven photometric measures, is characterized by a steep red slope increasing from 0.5 \micron to 1.6 \micron followed by a flattening of the spectrum at wavelengths $>$ 1.6 \micron. We fit the spectrum with a model population of dust grains made of tholins, materials comprised of complex organic materials seen throughout the outer parts of our Solar System. The presence of organic material around a star that may be in the later stages of giant planet formation implies that the basic building blocks for life may be common in planetary systems., Comment: 5 pages, emulateapj, Accepted to ApJL

During planet formation, a gas giant will interact with smaller protoplanets that stray within its sphere of gravitational influence. We investigate the outcome of interactions between gas giants and terrestrial-sized protoplanets with lunar-sized companions. An interaction between a giant planet and a protoplanet binary may have one of several consequences, including the delivery of volatiles to the inner system, the capture of retrograde moons by the giant planet, and the ejection of one or both of the protoplanets. We show that an interesting fraction of terrestrial-sized planets with lunar sized companions will likely be ejected into interstellar space with the companion bound to the planet. The companion provides an additional source of heating for the planet from tidal dissipation of orbital and spin angular momentum. This heat flux typically is larger than the current radiogenic heating of the Earth for up to the first few hundred million years of evolution. In combination with an atmosphere of sufficient thickness and composition, the heating can provide the conditions necesary for liquid water to persist on the surface of the terrestrial mass planet, making it a potential site for life. We also determine the possibility for directly detecting such systems through all-sky infrared surveys or microlensing surveys. Microlensing surveys in particular will directly measure the frequency of this phenomenon., Comment: 4 pages, 2 figures, Accepted to ApJL

Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, require external accretion of material to explain the presence of weak metal line absorption in their photospheres. The source of this material is currently unknown, but could come from the interstellar medium, unseen companions, or relic planetesimals from asteroid belt or Kuiper belt analogues. Accurate mid-infrared photometry of these white dwarfs provide additional information to solve the mystery of this accretion and to look for evidence of planetary systems that have survived post main sequence evolution. We present {\em Spitzer} IRAC photometry accurate to $\sim$3% for four DAZs and one DA with circumstellar absorption lines in the UV. We search for excesses due to unseen companions or circumstellar dust disks. We use {\em Hubble Space Telescope} NICMOS imaging of these white dwarfs to gauge the level of background contamination to our targets as well as rule out common proper motion companions to WD 1620-391. All of our targets show no excesses due to companions $>$20 M$_{J}$, ruling out all but very low mass companions to these white dwarfs at all separations. No excesses due to circumstellar disks are observed, and we place limits on what types of disks may still be present., Comment: 18 pages, 8 figures, Accepted to AJ

Hydrogen atmosphere white dwarfs with metals, so-called DAZs, require external accretion of material to explain the presence of weak metal line absorption in their photospheres. The source of this material is currently uknown, but could come from the interstellar medium, unseen companions, or relic planetesimals from asteroid belt or Kuiper belt analogues. Mid-infrared photometry of these white dwarfs provide additional information to solve the mystery of this accretion and to look for evidence of planetary systems that have survived post main sequence evolution. We present {\em Spitzer} IRAC photometry of five DAZs and search for excesses due to unseen companions or circumstellar dust disks. Three of our targets show unexpected {\em deficits} in flux, which we tentatively attribute to absorption due to SiO and CO., Comment: 6 pages, 2 figures, 15th European WD conference

Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, show evidence for ongoing accretion of material onto their surfaces. Some DAZs are known to have unresolved M dwarf companions, which could account for the observed accretion through a stellar wind. I combine observed Ca abundances of the DAZs with information on the orbital separation of their M dwarf companions to infer the mass loss rate of the M dwarfs. I find that for three of the six known DAZs with M dwarf companions, a stellar wind can plausibly explain the observed accretion on the white dwarfs assuming Bondi-Hoyle accretion of solar abundance stellar winds on the order of 10$^{-14}-10^{-16}\Msun$ yr$^{-1}$. The rest of the sample have companions with orbits $\gtorder$ 1~AU, and require companion mass loss rates of $> 10^{-11}\Msun$ yr$^{-1}$. I conclude that there must be an alternative explanation for accretion of material onto DAZs with widely separated companions. The inferred winds for two of the close binaries are orders of magnitude smaller than typically assumed for the angular momentum loss of red dwarf-white dwarf pairs due to magnetic braking from a stellar wind and may seriously affect predictions for the formation rate of CVs with low mass companions., Comment: 18 pages, 3 figures, accepted to ApJ

We present near-infrared $JHK_s$ photometry and light curves of the candidate magnetic white dwarf+brown dwarf binary SDSS J121209.31+013627.7 and report on the detection of near-infrared excess and variability in the $K_s-$band. The observed near-infrared excess can be explained by the presence of an L7 brown dwarf and an extra emission source. The $J$ and $H$ light curves appear flat, which rules out eclipses deeper than 0.2 mag and the presence of an accretion hot spot on the white dwarf. From the variable $K_s$ lightcurve, we get a refined period for the system of 88$\pm$1 minutes. We show that the observed variability in $K_s-$band can be explained by cyclotron emission, which can be modeled by a small spot on the surface of the white dwarf. SDSS 1212 exhibits similarities to the ultra-short period polar EF Eridani, however the lack of evidence for Roche-lobe overflow accretion suggests it may be a pre-polar., Comment: 13 pages, 2 figures, accepted to ApJL

The recently discovered substellar companion to GQ Lup possibly represents a direct test of current planet formation theories. We examine the possible formation scenarios for the companion to GQ Lup assuming it is a $\sim$2 M$_{Jup}$ object. We determine that GQ Lup B most likely was scattered into a large, eccentric orbit by an interaction with another planet in the inner system. If this is the case, several directly observable predictions can be made, including the presence of a more massive, secondary companion that could be detected through astrometry, radial velocity measurements, or scuplting in GQ Lup's circumstellar disk. This scenario requires a highly eccentric orbit for the companion already detected. These predictions can be tested within the next decade or so. Additionally, we look at scenarios of formation if the companion is a brown dwarf. One possible formation scenario may involve an interaction between a brown dwarf binary and GQ Lup. We look for evidence of any brown dwarfs that have been ejected from the GQ Lup system by searching the 2MASS all-sky survey., Comment: 6 pages, submitted to A&A

Results from a groundbased high contrast imaging survey of thirteen nearby white dwarfs for substellar objects is presented. We place strict upper limits on the type of substellar objects present, ruling out the presence of anything larger than $\sim$14 M$_{Jup}$ for eight of the white dwarfs at separations $>$19 AU and corresponding to primordial separations of $\sim$3-6~AU assuming adiabatic mass loss without tidal interactions. With these results we place the first upper limit on the number of intermediate mass stars with brown dwarfs at separations $>$ 13 AU. We combine these results with previous work to place upper limits on the number of massive Jovian ($>$ 10 M$_{Jup}$) planets in orbit around white dwarfs whose progenitors spanned a mass range of 1-7 M$_{\odot}$., Comment: 20 pages, 6 figures, Accepted to AJ, minor edits

Results from a concerted Hubble Space Telescope (HST) survey of nearby white dwarfs for substellar objects is presented. A total of 7 DAZ white dwarfs with distances of $<$ 50 pc had high contrast and high spatial resolution NICMOS coronagraphic images taken to search for candidate substellar objects at separations $\ltorder$10\arcsec away. Limits to unresolved companions are derived through analysis of 2MASS photometry of the white dwarfs compared to expected fluxes based on the WDs effective temperature, distance, and gravity. From our survey with HST we find several candidate companions, which have been or will be followed up with second epoch observations. We find that for four of the white dwarfs we are sensitive to planetary companions $\gtorder$10 M$_{Jup}$, and sensitive to companions $>$ 18 M$_{Jup}$ for all of the targets. The lack of significant near infrared excesses for our targets limits any kind of unresolved companions present to be substellar. In light of these results we make several comments on the possibility of determining the origin of white dwarfs with metals in their atmospheres., Comment: 11 pages, 7 figures, emulateapj, revisions to figures and text, to appear in September AJ

We present high contrast images of the hydrogen white dwarf G 29-38 taken in the near infrared with the Hubble Space Telescope and the Gemini North Telescope as part of a high contrast imaging search for substellar objects in orbit around nearby white dwarfs. We review the current limits on planetary companions for G29-38, the only nearby white dwarf with an infrared excess due to a dust disk. We add our recent observations to these limits to produce extremely tight constraints on the types of possible companions that could be present. No objects $>$ 6 M$_{Jup}$ are detected in our data at projected separations $>$ 12 AU, and no objects $>$ 16 M$_{Jup}$ are detected for separations from 3 to 12 AU, assuming a total system age of 1 Gyr. Limits for companions at separations $<$ 3 AU come from a combination of 2MASS photometry and previous studies of G29-38's pulsations. Our imaging with Gemini cannot confirm a tentative claim for the presence of a low mass brown dwarf. These observations demonstrate that a careful combination of several techniques can probe nearby white dwarfs for large planets and low mass brown dwarfs., Comment: 20 pages, 4 figures, Accepted to ApJ

Gaussian aperture pupil masks (GAPMs) can in theory achieve the contrast requisite for directly imaging an extrasolar planet around a nearby solar type star. We outline the process of designing, fabricating, and testing a GAPM for use on current telescopes and specifically the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. We find that the initial prototype observations are quite successful, achieving a contrast similar to a traditional Lyot coronagraph without blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab we can reproduce the expected PSF reasonably well and with a single aperture design which achieves $\sim4 \times 10^{-5}$ contrast at 10$\lambda/D$. We find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribute the most degradation to contrast at these levels., Comment: 19 pages, 5 figures, accepted to PASP

We present the first laboratory experiments using a notch-filter mask, a coronagraphic image mask that can produce infinite dynamic range in an ideal Lyot coronagraph according to scalar diffraction theory. We fabricated the first notch-filter mask prototype with .25 $\micron$ precision using an e-beam lithography machine. Our initial optical tests show that the prototype masks generate contrast levels of 10$^{-5}$ at 3$\lambda/D$ and 10$^{-6}$ at $\sim 8\lambda/D$, with a throughput of 27%. We speculate on the ``as-is'' performance of such a mask in the Hubble Space Telescope., Comment: 12 pages, 4 figures, Accepted to ApJ

Gaussian aperture pupil masks (GAPMs) can in theory achieve the contrast requisite for directly imaging an extrasolar planet. We outline the process of fabricating and testing a GAPM for use on the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. We find that the initial prototype observations are quite successful, achieving a contrast similar to a traditional Lyot coronagraph witho ut blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab we can reproduce the expected PSF to within an order of magnitude and with new designs achieve $\sim5 \times 10^{-5}$ contrast at 10$\lambda/D$. We find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribute the most degradation to contrast. Finally we compare the performance of GAPMs and Lyot coronagraphs of similar throughput., Comment: 11 pages, 10 figures, to appear in Proc. SPIE Vol. 4860

Placing a pupil mask with a gaussian aperture into the optical train of current telescopes represents a way to attain high contrast imaging that potentially improves contrast by orders of magnitude compared to current techniques. We present here the first observations ever using a gaussian aperture pupil mask (GAPM) on the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. Two nearby stars were observed, $\epsilon$ Eridani and $\mu$ Her A. A faint companion was detected around $\mu$ Her A, confirming it as a proper motion companion. Furthermore, the observed H and K magnitudes of the companion were used to constrain its nature. No companions or faint structure were observed for $\epsilon$ Eridani. We found that our observations with the GAPM achieved contrast levels similar to our coronographic images, without blocking light from the central star. The mask's performance also nearly reached sensitivities reported for other ground based adaptive optics coronographs and deep HST images, but did not reach theoretically predicted contrast levels. We outline ways that could improve the performance of the GAPM by an order of magnitude or more., Comment: 8 pages, 4 figures, accepted by ApJ letters

High spatial resolution (0.30 arcsec) NIR photometric observations using the adaptive optics of the 100 inch Mt. Wilson Telescope and the Penn State IR Imager and Spectrograph (PIRIS) have revealed faint companions to HD190067 and HIP13855. HD190067b is found to be of mass of 0.075$M_{\odot}$ to 0.1$M_{\odot}$ and with an age of 0.5 Gyrs to a few Gyrs. HIP13855b is a low mass star (age: 100 Myrs to 500 Myrs) of mass range between 0.1$M_{\odot}$ to 0.2$M_{\odot}$. Further NIR spectroscopic observations will be necessary to classify their spectral type precisely., Comment: 14 pages, 5 Figures, Accepted in the Astronomical Journal for publication