arXiv subjects

John H. Debes

Publications and source records attributed to John H. Debes.

60 records · Page 4Linked to original sources

arXiv2012

The WIRED Survey III: An Infrared Excess around the Eclipsing Post-Common Envelope Binary SDSS J030308.35+005443.7

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.

astro-ph.SR↗

arXiv2010

Too Little, Too Late: How the Tidal Evolution of Hot Jupiters affects Transit Surveys of Clusters

The tidal evolution of hot Jupiters may change the efficiency of transit surveys of stellar clusters. The orbital decay that hot Jupiters suffer may result in their destruction, leaving fewer transiting planets in older clusters. We calculate the impact tidal evolution has for different assumed stellar populations, including that of 47~Tuc, a globular cluster that was the focus of an intense HST search for transits. We find that in older clusters one expects to detect fewer transiting planets by a factor of two for surveys sensitive to Jupiter-like planets in orbits out to 0.5~AU, and up to a factor of 25 for surveys sensitive to Jupiter-like planets in orbits out to 0.08~AU. Additionally, tidal evolution affects the distribution of transiting planets as a function of semi-major axis, producing larger orbital period gaps for transiting planets as the age of the cluster increases. Tidal evolution can explain the lack of detected exoplanets in 47~Tuc without invoking other mechanisms. Four open clusters residing within the {\em Kepler} fields of view have ages that span 0.4-8~Gyr--if {\em Kepler} can observe a significant number of planets in these clusters, it will provide key tests for our tidal evolution hypothesis. Finally, our results suggest that observers wishing to discover transiting planets in clusters must have sufficient accuracy to detect lower mass planets, search larger numbers of cluster members, or have longer observation windows to be confident that a significant number of transits will occur for a population of stars.

astro-ph.EP↗

arXiv2010

Strong Constraints to the Putative Planet Candidate around VB 10 using Doppler spectroscopy

We present new radial velocity measurements of the ultra-cool dwarf VB 10, which was recently announced to host a giant planet detected with astrometry. The new observations were obtained using optical spectrographs(MIKE/Magellan and ESPaDOnS/CHFT) and cover a 63% of the reported period of 270 days. We apply Least-squares periodograms to identify the most significant signals and evaluate their corresponding False Alarm Probabilities. We show that this method is the proper generalization to astrometric data because (1) it mitigates the coupling of the orbital parameters with the parallax and proper motion, and (2) it permits a direct generalization to include non-linear Keplerian parameters in a combined fit to astrometry and radial velocity data. In fact, our analysis of the astrometry alone uncovers the reported 270 d period and an even stronger signal at 50 days. We estimate the uncertainties in the parameters using a Markov Chain Monte Carlo approach. The nominal precision of the new Doppler measurements is about 150 s$^{-1}$ while their standard deviation is 250 ms$^{-1}$. However, the best fit solutions still have RMS of 200 ms$^{-1}$ indicating that the excess in variability is due to uncontrolled systematic errors rather than the candidate companions detected in the astrometry. Although the new data alone cannot rule-out the presence of a candidate, when combined with published radial velocity measurements, the False Alarm Probabilities of the best solutions grow to unacceptable levels strongly suggesting that the observed astrometric wobble is not due to an unseen companion.

astro-ph.EP↗

arXiv2004

Finding Extrasolar Planets in the Stellar Graveyard with the Hubble Space Telescope

In order to directly image an extrasolar planet, the large contrast between a star and a companion planet must be overcome. White Dwarfs (WDs) are the remnants of stars > 1 M_sun and are orders of magnitude dimmer, making searches for planets and brown dwarfs (BDs) possible. We present the preliminary results of a survey of 7 hydrogen white dwarfs with photospheric metal lines (DAZs) for substellar and planetary objects, using NICMOS on the Hubble Space Telescope (HST). The extremely high contrast available with the NICMOS coronagraph allows 7-12 M_Jup planets to be detected to within 10-30 AU of the primary WD. This represents the first concerted search for planetary objects around stars that were more massive than the sun. Our results show that there are candidates around three of the seven stars, which are awaiting confirmation through common proper motion studies, some of which can only be confirmed through another observation with HST. Continuing studies of WDs will constrain planet formation scenarios for more massive stars and provide a sample of planets to study with future space missions such as JWST and SIM.

astro-ph↗

arXiv2003

High Contrast Imaging of Extrasolar Planets

Gaussian aperture pupil masks (GAPMs) can in theory achieve the contrast requisite for directly imaging an extrasolar planet. We use lab tests and simulations to further study their possible place as a high contrast imaging technique. We present lab comparisons with traditional Lyot coronagraphs and simulations of GAPMs and other high contrast imaging techniques on HST.

astro-ph↗

arXiv2002

Are There Unstable Planetary Systems Around White Dwarfs?

The presence of planets around solar-type stars suggests that many white dwarfs should have relic planetary systems. While planets closer than $\sim$ 5~AU will most likely not survive the post-main sequence lifetime of its parent star, any planet with semimajor axis $>$ 5~AU will survive, and its semimajor axis will increase as the central star loses mass. Since the stability of adjacent orbits to mutual planet-planet perturbations depends on the ratio of the planet mass to the central star's mass, some planets in previously stable orbits around a star undergoing mass loss will become unstable. We show that when mass loss is slow, systems of two planets that are marginally stable can become unstable to close encounters, while for three planets the timescale for close approaches decreases significantly with increasing mass ratio. These processes could explain the presence of anomalous IR excesses around white dwarfs that cannot be explained by close companions, such as G29-38, and may also be an important factor in explaining the existence of DAZ white dwarfs. The onset of instability through changing mass-ratios will also be a significant effect for planetary embryos gaining mass in protoplanetary disks.

astro-ph↗