arXiv subjects

Dawn M. Gelino

Publications and source records attributed to Dawn M. Gelino.

35 records · Page 2Linked to original sources

arXiv2011

Detectability of Exoplanet Periastron Passage in the Infra-Red

Characterization of exoplanets has matured in recent years, particularly through studies of exoplanetary atmospheres of transiting planets at infra-red wavelenegths. The primary source for such observations has been the Spitzer Space Telescope but these studies are anticipated to continue with the James Webb Space Telescope (JWST). A relatively unexplored region of exoplanet parameter space is the thermal detection of long-period eccentric planets during periastron passage. Here we describe the thermal properties and albedos of long-period giant planets along with the eccentricities of those orbits which allow them to remain within the habitable zone. We further apply these results to the known exoplanets by calculating temperatures and flux ratios for the IRAC passbands occupied by warm Spitzer, considering both low and high thermal redistribution efficiencies from the perspective of an observer. We conclude with recommendations on which targets are best suited for follow-up observations.

astro-ph.EP↗

arXiv2011

TERMS Photometry of Known Transiting Exoplanets

The Transit Ephemeris Refinement and Monitoring Survey (TERMS) conducts radial velocity and photometric monitoring of known exoplanets in order to refine planetary orbits and predictions of possible transit times. This effort is primarily directed towards planets not known to transit, but a small sample of our targets consist of known transiting systems. Here we present precision photometry for 6 WASP planets acquired during their transit windows. We perform a Markov Chain Monte Carlo (MCMC) analysis for each planet and combine these data with previous measurements to redetermine the period and ephemerides for these planets. These observations provide recent mid-transit times which are useful for scheduling future observations. Our results improve the ephemerides of WASP-4b, WASP-5b and WASP-6b and reduce the uncertainties on the mid-transit time for WASP-29b. We also confirm the orbital, stellar and planetary parameters of all 6 systems.

astro-ph.EP↗

arXiv2011

Planetary Phase Variations of the 55 Cancri System

Characterization of the composition, surface properties, and atmospheric conditions of exoplanets is a rapidly progressing field as the data to study such aspects become more accessible. Bright targets, such as the multi-planet 55 Cancri system, allow an opportunity to achieve high signal-to-noise for the detection of photometric phase variations to constrain the planetary albedos. The recent discovery that that inner-most planet, 55 Cancri e, transits the host star introduces new prospects for studying this system. Here we calculate photometric phase curves at optical wavelengths for the system with varying assumptions for the surface and atmospheric properties of 55 Cancri e. We show that the large differences in geometric albedo allows one to distinguish between various surface models, that the scattering phase function cannot be constrained with foreseeable data, and that planet b will contribute significantly to the phase variation depending upon the surface of planet e. We discuss detection limits and how these models may be used with future instrumentation to further characterize these planets and distinguish between various assumptions regarding surface conditions.

astro-ph.EP↗

arXiv2011

On the Inclination Dependence of Exoplanet Phase Signatures

Improved photometric sensitivity from space-based telescopes have enabled the detection of phase variations for a small sample of hot Jupiters. However, exoplanets in highly eccentric orbits present unique opportunities to study the effects of drastically changing incident flux on the upper atmospheres of giant planets. Here we expand upon previous studies of phase functions for these planets at optical wavelengths by investigating the effects of orbital inclination on the flux ratio as it interacts with the other effects induced by orbital eccentricity. We determine optimal orbital inclinations for maximum flux ratios and combine these calculations with those of projected separation for application to coronagraphic observations. These are applied to several of the known exoplanets which may serve as potential targets in current and future coronagraph experiments.

astro-ph.EP↗

arXiv2010

Photometric Phase Variations of Long-Period Eccentric Planets

The field of exoplanetary science has diversified rapidly over recent years as the field has progressed from exoplanet detection to exoplanet characterization. For those planets known to transit, the primary transit and secondary eclipse observations have a high yield of information regarding planetary structure and atmospheres. The current restriction of these information sources to short-period planets may be abated in part through refinement of orbital parameters. This allows precision targeting of transit windows and phase variations which constrain the dynamics of the orbit and the geometric albedo of the atmosphere. Here we describe the expected phase function variations at optical wavelengths for long-period planets, particularly those in the high-eccentricity regime and multiple systems in resonant and non-coplanar orbits. We apply this to the known exoplanets and discuss detection prospects and how observations of these signatures may be optimized by refining the orbital parameters.

astro-ph.EP↗

arXiv2010

Modeling Multi-Wavelength Stellar Astrometry. II. Determining Absolute Inclinations, Gravity Darkening Coefficients, and Spot Parameters of Single Stars with SIM Lite

We present a novel technique to determine the absolute inclination of single stars using multi-wavelength sub-milliarcsecond astrometry. The technique exploits the effect of gravity darkening, which causes a wavelength-dependent astrometric displacement parallel to a star's projected rotation axis. We find this effect is clearly detectable using SIM Lite for various giant stars and rapid rotators, and present detailed models for multiple systems using the REFLUX code. We also explore the multi-wavelength astrometric reflex motion induced by spots on single stars. We find that it should be possible to determine spot size, relative temperature, and some positional information for both giant and nearby main-sequence stars utilizing multi-wavelength SIM Lite data. This data will be extremely useful in stellar and exoplanet astrophysics, as well as supporting the primary SIM Lite mission through proper multi-wavelength calibration of the giant star astrometric reference frame, and reduction of noise introduced by starspots when searching for extrasolar planets.

astro-ph.SR↗

arXiv2010

Modeling Multi-Wavelength Stellar Astrometry. I. SIM Lite Observations of Interacting Binaries

Interacting binaries consist of a secondary star which fills or is very close to filling its Roche lobe, resulting in accretion onto the primary star, which is often, but not always, a compact object. In many cases, the primary star, secondary star, and the accretion disk can all be significant sources of luminosity. SIM Lite will only measure the photocenter of an astrometric target, and thus determining the true astrometric orbits of such systems will be difficult. We have modified the Eclipsing Light Curve code (Orosz & Hauschildt 2000) to allow us to model the flux-weighted reflex motions of interacting binaries, in a code we call REFLUX. This code gives us sufficient flexibility to investigate nearly every configuration of interacting binary. We find that SIM Lite will be able to determine astrometric orbits for all sufficiently bright interacting binaries where the primary or secondary star dominates the luminosity. For systems where there are multiple components that comprise the spectrum in the optical bandpass accessible to SIM Lite, we find it is possible to obtain absolute masses for both components, although multi-wavelength photometry will be required to disentangle the multiple components. In all cases, SIM Lite will at least yield accurate inclinations, and provide valuable information that will allow us to begin to understand the complex evolution of mass-transferring binaries. It is critical that SIM Lite maintains a multi-wavelength capability to allow for the proper deconvolution of the astrometric orbits in multi-component systems.

astro-ph.SR↗

arXiv2010

The Inclination of the Soft X-ray Transient A0620--00 and the Mass of its Black Hole

We analyze photometry of the Soft X-ray Transient A0620-00 spanning nearly 30 years, including previously published and previously unpublished data. Previous attempts to determine the inclination of A0620 using subsets of these data have yielded a wide range of measured values of i. Differences in the measured value of i have been due to changes in the shape of the light curve and uncertainty regarding the contamination from the disk. We give a new technique for estimating the disk fraction and find that disk light is significant in all light curves, even in the infrared. We also find that all changes in the shape and normalization of the light curve originate in a variable disk component. After accounting for this disk component, we find that all the data, including light curves of significantly different shapes, point to a consistent value of i. Combining results from many separate data sets, we find i=51 plus or minus 0.9 degrees, implying M=6.6 plus or minus 0.25 solar masses. Using our dynamical model and zero-disk stellar VIH magnitudes, we find d=1.06 plus or minus 0.12 kpc. Understanding the disk origin of non-ellipsoidal variability may assist with making reliable determinations of i in other systems, and the fluctuations in disk light may provide a new observational tool for understanding the three-dimensional structure of the accretion disk.

astro-ph.HE↗

arXiv2007

Uncovering the Nature of the X-ray Transient 4U 1730-22: Discovery of X-ray Emission from a Neutron Star in Quiescence with Chandra

The X-ray transient, 4U 1730-22, has not been detected in outburst since 1972, when a single outburst was detected by the Uhuru satellite. This neutron star or black hole X-ray binary is presumably in quiescence now, and here, we report on X-ray and optical observations of the 4U 1730-22 field designed to identify the system's quiescent counterpart. Using Chandra, we have found a very likely counterpart. The candidate counterpart is close to the center of the Uhuru error region and has a thermal spectrum. The 0.3-8 keV spectrum is well-described by a neutron star atmosphere model with an effective temperature of 131+/-21 eV. For a neutron star with a 10 km radius, the implied source distance is 10(+12)(-4) kpc, and the X-ray luminosity is 1.9E33 ergs/s assuming a distance of 10 kpc. Accretion from a companion star is likely required to maintain the temperature of this neutron star, which would imply that it is an X-ray binary and therefore, almost certainly the 4U 1730-22 counterpart. We do not detect an optical source at the position of the Chandra source down to R > 22.1, and this is consistent with the system being a Low-Mass X-ray Binary at a distance greater than a few kpc. If our identification is correct, 4U 1730-22 is one of the 5 most luminous of the 20 neutron star transients that have quiescent X-ray luminosity measurements.

astro-ph↗

arXiv2006

The UCSD Radio-Selected Quasar Survey for Damped Lyman alpha System

As large optical quasar surveys for damped Lya become a reality and the study of star forming gas in the early Universe achieves statistical robustness, it is now vital to identify and quantify the sources of systematic error. Because the nature of optically-selected quasar surveys makes them vulnerable to dust obscuration, we have undertaken a radio-selected quasar survey for damped Lya systems to address this bias. We present the definition and results of this survey. We then combine our sample with the CORALS dataset to investigate the HI column density distribution function f(N) of damped Lya systems toward radio-selected quasars. We find that f(N) is well fit by a power-law f(N) = k_1 N^alpha_1, with log k_1 = 22.90 and alpha_1 = -2.18. This power-law is in excellent agreement with that of optically-selected samples at low N(HI), an important yet expected result given that obscuration should have negligible effect at these gas columns. However, because of the relatively small size of the radio-selected sample, 26 damped Lya systems in 119 quasars, f(N) is not well constrained at large N(HI) and the first moment of the HI distribution function, Omega_g, is, strictly speaking, a lower limit. The power-law is steep enough, however, that extrapolating it to higher column densities implies only a modest, logarithmic increase in Omega_g. The radio-selected value of Omega_g = 1.15 x 10^-3, agrees well with the results of optically-selected surveys. While our results indicate that dust obscuration is likely not a major issue for surveys of damped Lya systems, we estimate that a radio-selected sample of approximately 100 damped Lya systems will be required to obtain the precision necessary to absolutely confirm an absence of dust bias.

astro-ph↗

arXiv2006

The Inclination Angle of and Mass of the Black Hole in XTE J1118+480

We have obtained optical and infrared photometry of the quiescent soft X-ray transient XTE J1118+480. In addition to optical and J-band variations, we present the first observed H- and K_s-band ellipsoidal variations for this system. We model the variations in all bands simultaneously with the WD98 light curve modeling code. The infrared colors of the secondary star in this system are consistent with a K7V, while there is evidence for light from the accretion disk in the optical. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 68 +/- 2 deg. This inclination angle corresponds to a primary black hole mass of 8.53 +/- 0.60 M_sun. Based on the derived physical parameters and infrared colors of the system, we determine a distance of 1.72 +/- 0.10 kpc to XTE J1118+480.

astro-ph↗

arXiv2005

The Low Quiescent X-Ray Luminosity of the Transient X-Ray Burster EXO 1747-214

We report on X-ray and optical observations of the X-ray burster EXO 1747-214. This source is an X-ray transient, and its only known outburst was observed in 1984-1985 by the EXOSAT satellite. We re-analyzed the EXOSAT data to derive the source position, column density, and a distance upper limit using its peak X-ray burst flux. We observed the EXO 1747-214 field in 2003 July with the Chandra X-ray Observatory to search for the quiescent counterpart. We found one possible candidate just outside the EXOSAT error circle, but we cannot rule out the possibility that the source is unrelated to EXO 1747-214. Our conclusion is that the upper limit on the unabsorbed 0.3-8 keV luminosity is L < 7E31 erg/s, making EXO 1747-214 one of the faintest neutron star transients in quiescence. We compare this luminosity upper limit to the quiescent luminosities of 19 neutron star and 14 black hole systems and discuss the results in the context of the differences between neutron stars and black holes. Based on the theory of deep crustal heating by Brown and coworkers, the luminosity implies an outburst recurrence time of >1300 yr unless some form of enhanced cooling occurs within the neutron star. The position of the possible X-ray counterpart is consistent with three blended optical/IR sources with R-magnitudes between 19.4 and 19.8 and J-magnitudes between 17.2 and 17.6. One of these sources could be the quiescent optical/IR counterpart of EXO 1747-214.

astro-ph↗

arXiv2004

The Low Quiescent X-Ray Luminosity of the Neutron Star Transient XTE J2123-058

We report on the first X-ray observations of the neutron star soft X-ray transient (SXT) XTE J2123-058 in quiescence, made by Chandra and BeppoSAX, as well as contemporaneous optical observations. In 2002, the Chandra spectrum of XTE J2123-058 is consistent with a power-law model, or the combination of a blackbody plus a power-law, but it is not well-described by a pure blackbody. Using the interstellar column density, the power-law fit gives photon index of 3.1 (+0.7,-0.6) and indicates a 0.3-8 keV unabsorbed luminosity of 9(+4,-3)E31 (d/8.5 kpc)^2 ergs/s (90% confidence errors). Fits with models consisting of thermal plus power-law components indicate that the upper limit on the temperature of a 1.4 solar mass, 10 km radius neutron star with a hydrogen atmosphere is kT_eff < 66 eV, and the upper limit on the bolometric luminosity is L_infinity < 1.4E32 ergs/s, assuming d = 8.5 kpc. Of the neutron star SXTs that exhibit short (< 1 year) outbursts, including Aql X-1, 4U 1608-522, Cen X-4, and SAX J1810.8-2609, the lowest temperatures and luminosities are found for XTE J2123-058 and SAX J1810.8-2609. From the BeppoSAX observation of XTE J2123-058 in 2000, we obtained an upper limit on the 1-10 keV unabsorbed luminosity of 9E32 ergs/s. Although this upper limit allows that the X-ray luminosity may have decreased between 2000 and 2002, that possibility is not supported by our contemporaneous R-band observations, which indicate that the optical flux increased significantly. Motivated by the theory of deep crustal heating by Brown and co-workers, we characterize the outburst histories of the five SXTs. The low quiescent luminosity for XTE J2123-058 is consistent with the theory of deep crustal heating without requiring enhanced neutron star cooling if the outburst recurrence time is >~ 70 years.

astro-ph↗

arXiv2003

GRO J0422+32: The Lowest Mass Black Hole?

We have obtained optical and infrared photometry of the soft X-ray transient GRO J0422+32. From this photometry, we find a secondary star spectral type of M1, and an extinction of Av = 0.74 +/- 0.09. We present the first observed infrared (J-, H-, and K-band) ellipsoidal variations, and model them with WD98, a recent version of the Wilson-Devinney light curve modeling code. Assuming no significant contamination of the infrared light curves, we find a lower limit to the inclination angle of 43 degrees corresponding to an upper limit on the mass of the compact object of 4.92 M_sun. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 45 +/- 2 degrees. This inclination angle corresponds to a primary black hole mass of 3.97 +/- 0.95 M_sun. Thus we contend that J0422+32 contains the lowest mass stellar black hole reported, and the first to have a measured mass that falls in the 3 - 5 M_sun range.

astro-ph↗

arXiv2001

A Multi-Wavelength, Multi-Epoch Study of the Soft X-Ray Transient Prototype, V616 Mon (A0620-00)

We have obtained optical and infrared photometry of the soft x-ray transient prototype V616 Mon (A0620-00). From this photometry, we find a spectral type of K4 for the secondary star in the system, which is consistent with spectroscopic observations. We present J-, H-, and K-band light curves modeled with WD98 and ELC. Combining detailed, independently run models for ellipsoidal variations due to a spotted, non-spherical secondary star, and the observed ultraviolet to infrared spectral energy distribution of the system, we show that the most likely value for the orbital inclination is 40.75 +/- 3 deg. This inclination angle implies a primary black hole mass of 11.0 +/- 1.9 solar masses.

astro-ph↗

arXiv2001

Infrared Observations of Nova Muscae 1991: Black Hole Mass Determination from Ellipsoidal Variations

We have obtained infrared photometry for the soft x-ray transient GU Mus. We present J and K_s band light curves modeled with WD98, the newest version of the Wilson-Devinney light curve modeling code. Using detailed models for the expected ellipsoidal variations due to the non-spherical secondary star, we show that the most likely value for the orbital inclination is 54 +/-1.5 deg. This inclination angle is consistent with those previously published, but has a much smaller error. This inclination implies a primary black hole mass of 6.95 +/-0.6 M_sun. While we do not see any evidence for contamination of our infrared light curves from other sources in the system, a conservative model with a contamination level of 15% increases the uncertainty in the inclination angle to 54 +4/-1.5 deg.

astro-ph↗

arXiv2000

Infrared Observations of AR Ursae Majoris: Modeling the Ellipsoidal Variations

We have obtained time-series infrared photometry for the highly magnetic cataclysmic variable AR UMa. Our J and K' band observations occurred during a low state and they show a distinctive double-humped structure. Using detailed models for the expected ellipsoidal variations in the infrared due to the non-spherical secondary star, we find that the most likely value for the system inclination is 70 degrees. We also model low state V band photometry and find that its observed double-humped structure is not caused by ellipsoidal variations, as they have been ascribed to, but are due to beamed cyclotron radiation. We use this result to estimate the magnetic field strength of the active southern accretion region (B <= 190 MG) and its magnetic longitude (330 degrees).

astro-ph↗