arXiv subjects

H. Isaacson

Publications and source records attributed to H. Isaacson.

At least 55 records · Page 3Linked to original sources

arXiv2017

KIC 8164262: a Heartbeat Star Showing Tidally Induced Pulsations with Resonant Locking

We present the analysis of KIC 8164262, a heartbeat star with a high-amplitude (~1 mmag), tidally resonant pulsation (a mode in resonance with the orbit) at 229 times the orbital frequency and a plethora of tidally induced g-mode pulsations (modes excited by the orbit). The analysis combines Kepler light curves with follow-up spectroscopic data from the Keck telescope, KPNO (Kitt Peak National Observatory) 4-m Mayal telescope and the 2.7-m telescope at the McDonald observatory. We apply the binary modelling software, PHOEBE, to the Kepler light curve and radial velocity data to determine a detailed binary star model that includes the prominent pulsation and Doppler boosting, alongside the usual attributes of a binary star model (including tidal distortion and reflection). The results show that the system contains a slightly evolved F star with an M secondary companion in a highly eccentric orbit (e = 0.886). We use the results of the binary star model in a companion paper (Fuller et al., 2017) where we show that the prominent pulsation can be explained by a tidally excited oscillation mode held near resonance by a resonance locking mechanism.

astro-ph.SR↗

arXiv2017

HAT-P-67b: An Extremely Low Density Saturn Transiting an F-Subgiant Confirmed via Doppler Tomography

We report the discovery of HAT-P-67b, a hot-Saturn transiting a rapidly rotating F-subgiant. HAT-P-67b has a radius of Rp = 2.085 -0.071/+0.096 RJ,, orbiting a M* = 1.642 -0.072/+0.155 Msun, R* = 2.546 -0.084/+0.099 Rsun host star in a ~4.81-day period orbit. We place an upper limit on the mass of the planet via radial velocity measurements to be Mp < 0.59 MJ, and lower limit of > 0.056 MJ by limitations on Roche lobe overflow. Despite being a subgiant, the host star still exhibits relatively rapid rotation, with a projected rotational velocity of v sin I* = 35.8 +/- 1.1 km/s, making it difficult to precisely determine the mass of the planet using radial velocities. We validated HAT-P-67b via two Doppler tomographic detections of the planetary transit, which eliminated potential eclipsing binary blend scenarios. The Doppler tomographic observations also confirmed that HAT-P-67b has an orbit that is aligned to within 12 degrees, in projection, with the spin of its host star. HAT-P-67b receives strong UV irradiation, and is amongst the one of the lowest density planets known, making it a good candidate for future UV transit observations to search for an extended hydrogen exosphere.

astro-ph.EP↗

arXiv2017

EPIC 220204960: A Quadruple Star System Containing Two Strongly Interacting Eclipsing Binaries

We present a strongly interacting quadruple system associated with the K2 target EPIC 220204960. The K2 target itself is a Kp = 12.7 magnitude star at Teff ~ 6100 K which we designate as "B-N" (blue northerly image). The host of the quadruple system, however, is a Kp = 17 magnitude star with a composite M-star spectrum, which we designate as "R-S" (red southerly image). With a 3.2" separation and similar radial velocities and photometric distances, 'B-N' is likely physically associated with 'R-S', making this a quintuple system, but that is incidental to our main claim of a strongly interacting quadruple system in 'R-S'. The two binaries in 'R-S' have orbital periods of 13.27 d and 14.41 d, respectively, and each has an inclination angle of >89 degrees. From our analysis of radial velocity measurements, and of the photometric lightcurve, we conclude that all four stars are very similar with masses close to 0.4 Msun. Both of the binaries exhibit significant ETVs where those of the primary and secondary eclipses 'diverge' by 0.05 days over the course of the 80-day observations. Via a systematic set of numerical simulations of quadruple systems consisting of two interacting binaries, we conclude that the outer orbital period is very likely to be between 300 and 500 days. If sufficient time is devoted to RV studies of this faint target, the outer orbit should be measurable within a year.

astro-ph.SR↗

arXiv2015

HATS-15 b and HATS-16 b: Two massive planets transiting old G dwarf stars

We report the discovery of HATS-15 b and HATS-16 b, two massive transiting extrasolar planets orbiting evolved ($\sim 10$ Gyr) main-sequence stars. The planet HATS-15 b, which is hosted by a G9V star ($V=14.8$ mag), is a hot Jupiter with mass of $2.17\pm0.15\, M_{\mathrm{J}}$ and radius of $1.105\pm0.0.040\, R_{\mathrm{J}}$, and completes its orbit in nearly 1.7 days. HATS-16 b is a very massive hot Jupiter with mass of $3.27\pm0.19\, M_{\mathrm{J}}$ and radius of $1.30\pm0.15\, R_{\mathrm{J}}$; it orbits around its G3 V parent star ($V=13.8$ mag) in $\sim2.7$ days. HATS-16 is slightly active and shows a periodic photometric modulation, implying a rotational period of 12 days which is unexpectedly short given its isochronal age. This fast rotation might be the result of the tidal interaction between the star and its planet.

astro-ph.EP↗

arXiv2015

A high obliquity orbit for the hot-Jupiter HATS-14b transiting a 5400K star

We report a spin-orbit misalignment for the hot-Jupiter HATS-14b, measuring a projected orbital obliquity of |lambda|= 76 -5/+4 deg. HATS-14b orbits a high metallicity, 5400 K G dwarf in a relatively short period orbit of 2.8 days. This obliquity was measured via the Rossiter-McLaughlin effect, obtained with observations from Keck-HIRES. The velocities were extracted using a novel technique, optimised for low signal-to-noise spectra, achieving a high precision of 4 m/s point-to-point scatter. However, we caution that our uncertainties may be underestimated. Due to the low rotational velocity of the star, the detection significance is dependent on the vsini prior that is imposed in our modelling. Based on trends observed in the sample of hot Jupiters with obliquity measurements, it has been suggested that these planets modify the spin axes of their host stars, with an efficiency that depends on the stellar type and orbital period of the system. In this framework, short-period planets around stars with surface convective envelopes, like HATS-14b, are expected to have orbits that are aligned with the spin axes of their host stars. HATS-14b, however, is a significant outlier from this trend, challenging the effectiveness of the tidal realignment mechanism.

astro-ph.EP↗

arXiv2015

HAT-P-57b: A Short-Period Giant Planet Transiting A Bright Rapidly Rotating A8V Star Confirmed Via Doppler Tomography

We present the discovery of HAT-P-57b, a P = 2.4653 day transiting planet around a V = 10.465 +- 0.029 mag, Teff = 7500 +- 250 K main sequence A8V star with a projected rotation velocity of v sin i = 102.1 +- 1.3 km s^-1. We measure the radius of the planet to be R = 1.413 +- 0.054 R_J and, based on RV observations, place a 95% confidence upper limit on its mass of M < 1.85 M_J . Based on theoretical stellar evolution models, the host star has a mass and radius of 1.47 +- 0.12 M_sun, and 1.500 +- 0.050 R_sun, respectively. Spectroscopic observations made with Keck-I/HIRES during a partial transit event show the Doppler shadow of HAT-P-57b moving across the average spectral line profile of HAT-P- 57, confirming the object as a planetary system. We use these observations, together with analytic formulae that we derive for the line profile distortions, to determine the projected angle between the spin axis of HAT-P-57 and the orbital axis of HAT-P-57b. The data permit two possible solutions, with -16.7 deg < lambda < 3.3 deg or 27.6 deg < lambda < 57.4 deg at 95% confidence, and with relative probabilities for the two modes of 26% and 74%, respectively. Adaptive optics imaging with MMT/Clio2 reveals an object located 2.7" from HAT-P-57 consisting of two point sources separated in turn from each other by 0.22". The H and L -band magnitudes of the companion stars are consistent with their being physically associated with HAT-P-57, in which case they are stars of mass 0.61 +- 0.10 M_sun and 0.53 +- 0.08 M_sun. HAT-P-57 is the most rapidly rotating star, and only the fourth main sequence A star, known to host a transiting planet.

astro-ph.EP↗

arXiv2015

The K2-ESPRINT Project. I. Discovery of the Disintegrating Rocky Planet K2-22b with a Cometary Head and Leading Tail

We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable transit depths, ranging from $\sim$0\% to 1.3\%, are suggestive of a planet that is disintegrating via the emission of dusty effluents. We characterize the host star as an M-dwarf with $T_{\rm eff} \simeq 3800$ K. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and (4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. The latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better statistical precision compared with the ground-based observations. We detect a significant "bump" just after the transit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context of a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet's Hill sphere and effectively undergo `Roche lobe overflow,' even though the planet's surface is likely underfilling its Roche lobe by a factor of 2.

astro-ph.EP↗

arXiv2015

HATS-7b: A Hot Super Neptune Transiting a Quiet K Dwarf Star

IW ../submit_V2/abstract.txt ( Row 1 Col 1 6:48 Ctrl-K H for help We report the discovery by the HATSouth network of HATS-7b, a transiting Super-Neptune with a mass of 0.120+/-0.012MJ, a radius of 0.563+/-(0.046,0.034)RJ, and an orbital period of 3.1853days. The host star is a moderately bright (V=13.340+/-0.010mag, K_S=10.976+/-0.026mag) K dwarf star with a mass of 0.849+/-0.027Msun , a radius of 0.815+/-(0.049,-0.035)Rsun, and a metallicity of [Fe/H]=+0.250+/-0.080. The star is photometrically quiet to within the precision of the HATSouth measurements and has low RV jitter. HATS-7b is the second smallest radius planet discovered by a wide-field ground-based transit survey, and one of only a handful of Neptune-size planets with mass and radius determined to 10% precision. Theoretical modeling of HATS-7b yields a hydrogen-helium fraction of 18+/-4% (rock-iron core and H2-He envelope), or 9+/-4% (ice core and H2-He envelope), i.e.it has a composition broadly similar to that of Uranus and Neptune, and very different from that of Saturn, which has 75% of its mass in H2-He. Based on a sample of transiting exoplanets with accurately (<20%) determined parameters, we establish approximate power-law relations for the envelopes of the mass-density distribution of exoplanets. HATS-7b, which, together with the recently discovered HATS-8b, is one of the first two transiting super-Neptunes discovered in the Southern sky, is a prime target for additional follow-up observations with Southern hemisphere facilities to characterize the atmospheres of Super-Neptunes (which we define as objects with mass greater than that of Neptune, and smaller than halfway between that of Neptune and Saturn, i.e. 0.054 MJ<Mp<0.18 MJ).

astro-ph.EP↗

arXiv2015

HATS-8b: A Low-Density Transiting Super-Neptune

HATS-8b is a low density transiting super-Neptune discovered as part of the HATSouth project. The planet orbits its solar-like G dwarf host (V=14.03 $\pm$ 0.10 and T$_{eff}$ =5679 $\pm$ 50 K) with a period of 3.5839 d. HATS-8b is the third lowest mass transiting exoplanet to be discovered from a wide-field ground based search, and with a mass of 0.138 $\pm$ 0.019 M$_J$ it is approximately half-way between the masses of Neptune and Saturn. However HATS-8b has a radius of 0.873 (+0.123,-0.075) R$_J$, resulting in a bulk density of just 0.259 $\pm$ 0.091 g.cm$^{-3}$. The metallicity of the host star is super-Solar ([Fe/H]=0.210 $\pm$ 0.080), arguing against the idea that low density exoplanets form from metal-poor environments. The low density and large radius of HATS-8b results in an atmospheric scale height of almost 1000 km, and in addition to this there is an excellent reference star of near equal magnitude at just 19 arcsecond separation on the sky. These factors make HATS-8b an exciting target for future atmospheric characterization studies, particularly for long-slit transmission spectroscopy.

astro-ph.EP↗

arXiv2015

KOI-3158: The oldest known system of terrestrial-size planets

The first discoveries of exoplanets around Sun-like stars have fueled efforts to find ever smaller worlds evocative of Earth and other terrestrial planets in the Solar System. While gas-giant planets appear to form preferentially around metal-rich stars, small planets (with radii less than four Earth radii) can form under a wide range of metallicities. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were far less abundant. We report Kepler spacecraft observations of KOI-3158, a metal-poor Sun-like star from the old population of the Galactic thick disk, which hosts five planets with sizes between Mercury and Venus. We used asteroseismology to directly measure a precise age of 11.2+/-1.0 Gyr for the host star, indicating that KOI-3158 formed when the Universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, providing scope for the existence of ancient life in the Galaxy.

astro-ph.EP↗

arXiv2015

An ancient extrasolar system with five sub-Earth-size planets

The chemical composition of stars hosting small exoplanets (with radii less than four Earth radii) appears to be more diverse than that of gas-giant hosts, which tend to be metal-rich. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were more scarce. We report Kepler spacecraft observations of Kepler-444, a metal-poor Sun-like star from the old population of the Galactic thick disk and the host to a compact system of five transiting planets with sizes between those of Mercury and Venus. We validate this system as a true five-planet system orbiting the target star and provide a detailed characterization of its planetary and orbital parameters based on an analysis of the transit photometry. Kepler-444 is the densest star with detected solar-like oscillations. We use asteroseismology to directly measure a precise age of 11.2+/-1.0 Gyr for the host star, indicating that Kepler-444 formed when the Universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, leaving open the possibility for the existence of ancient life in the Galaxy. The age of Kepler-444 not only suggests that thick-disk stars were among the hosts to the first Galactic planets, but may also help to pinpoint the beginning of the era of planet formation.

astro-ph.EP↗

arXiv2014

HAT-P-54b: A hot jupiter transiting a 0.64 Msun star in field 0 of the K2 mission

We report the discovery of HAT-P-54b, a planet transiting a late K dwarf star in field 0 of the NASA K2 mission. We combine ground-based photometric light curves with radial velocity measurements to determine the physical parameters of the system. HAT-P-54b has a mass of 0.760 $\pm$ 0.032 $M_J$, a radius of 0.944 $\pm$ 0.028 $R_J$, and an orbital period of 3.7998 d. The star has V = 13.505 $\pm$ 0.060, a mass of 0.645 $\pm$ 0.020 $M_{\odot}$, a radius of 0.617 $\pm$ 0.013 $R_{\odot}$, an effective temperature of Teff = 4390 $\pm$ 50K, and a subsolar metallicity of [Fe/H] = -0.127 $\pm$ 0.080. HAT-P-54b has a radius that is smaller than 92% of the known transiting planets with masses greater than that of Saturn, while HAT-P-54 is one of the lowest-mass stars known to host a hot Jupiter. Follow-up high-precision photometric observations by the K2 mission promise to make this a well-studied planetary system.

astro-ph.EP↗

arXiv2013

Kepler-62: A five-planet system with planets of 1.4 and 1.6 Earth radii in the Habitable Zone

We present the detection of five planets -- Kepler-62b, c, d, e, and f -- of size 1.31, 0.54, 1.95, 1.61 and 1.41 Earth radii, orbiting a K2V star at periods of 5.7, 12.4, 18.2, 122.4 and 267.3 days, respectively. The outermost planets (Kepler-62e & -62f) are super-Earth-size (1.25 < planet radius/earth radius < 2.0) planets in the habitable zone (HZ) of their host star, receiving 1.2 +- 0.2 and 0.41 +- 0.05 times the solar flux at Earth's orbit. Theoretical models of Kepler-62e and -62f for a stellar age of ~7 Gyr suggest that both planets could be solid: either with a rocky composition or composed of mostly solid water in their bulk.

astro-ph.EP↗

arXiv2013

Asteroseismic determination of obliquities of the exoplanet systems Kepler-50 and Kepler-65

Results on the obliquity of exoplanet host stars -- the angle between the stellar spin axis and the planetary orbital axis -- provide important diagnostic information for theories describing planetary formation. Here we present the first application of asteroseismology to the problem of stellar obliquity determination in systems with transiting planets and Sun-like host stars. We consider two systems observed by the NASA Kepler Mission which have multiple transiting small (super-Earth sized) planets: the previously reported Kepler-50 and a new system, Kepler-65, whose planets we validate in this paper. Both stars show rich spectra of solar-like oscillations. From the asteroseismic analysis we find that each host has its rotation axis nearly perpendicular to the line of sight with the sines of the angles constrained at the 1-sigma level to lie above 0.97 and 0.91, respectively. We use statistical arguments to show that coplanar orbits are favoured in both systems, and that the orientations of the planetary orbits and the stellar rotation axis are correlated.

astro-ph.EP↗

arXiv2012

Precise Radial Velocities of 2046 Nearby FGKM Stars and 131 Standards

We present radial velocities with an accuracy of 0.1 km/s for 2046 stars of spectral type F,G,K, and M, based on 29000 spectra taken with the Keck I telescope. We also present 131 FGKM standard stars, all of which exhibit constant radial velocity for at least 10 years, with an RMS less than 0.03 km/s. All velocities are measured relative to the solar system barycenter. Spectra of the Sun and of asteroids pin the zero-point of our velocities, yielding a velocity accuracy of 0.01 km/s for G2V stars. This velocity zero-point agrees within 0.01 \kms with the zero-points carefully determined by Nidever et al. (2002) and Latham et al. (2002). For reference we compute the differences in velocity zero-points between our velocities and standard stars of the IAU, the Harvard-Smithsonian Center for Astrophysics, and l'Observatoire de Geneve, finding agreement with all of them at the level of 0.1 km/s. But our radial velocities (and those of all other groups) contain no corrections for convective blueshift or gravitational redshifts (except for G2V stars), leaving them vulnerable to systematic errors of 0.2 \kms for K dwarfs and ~0.3 km/s for M dwarfs due to subphotospheric convection, for which we offer velocity corrections. The velocities here thus represent accurately the radial component of each star's velocity vector. The radial velocity standards presented here are designed to be useful as fundamental standards in astronomy. They may be useful for Gaia (Crifo et al. 2010, Gilmore et al. 2012} and for dynamical studies of such systems as long-period binary stars, star clusters, Galactic structure, and nearby galaxies, as will be carried out by SDSS, RAVE, APOGEE, SkyMapper, HERMES, and LSST.

astro-ph.GA↗

arXiv2011

The California Planet Survey III. A Possible 2:1 Resonance in the Exoplanetary Triple System HD 37124

We present new radial velocities from Keck Observatory and both Newtonian and Keplerian solutions for the triple-planet system orbiting HD 37124. The orbital solution for this system has improved dramatically since the third planet was first reported in Vogt et al. 2005 with an ambiguous orbital period. We have resolved this ambiguity, and the outer two planets have an apparent period commensurability of 2:1. A dynamical analysis finds both resonant and non-resonant configurations consistent with the radial velocity data, and constrains the mutual inclinations of the planets to be less than about 30 degrees. We discuss HD 37124 in the context of the other 19 exoplanetary systems with apparent period commenserabilities, which we summarize in a table. We show that roughly one in three well-characterized multiplanet systems has a apparent low-order period commensuribility, which is more than would naively be expected if the periods of exoplanets in known multiplanet systems were drawn randomly from the observed distribution of planetary orbital periods.

astro-ph.EP↗

arXiv2010

HAT-P-26b: A Low-Density Neptune-Mass Planet Transiting a K Star

We report the discovery of HAT-P-26b, a transiting extrasolar planet orbiting the moderately bright V=11.744 K1 dwarf star GSC 0320-01027, with a period P = 4.234516 +- 0.000015 d, transit epoch Tc = 2455304.65122 +- 0.00035 (BJD), and transit duration 0.1023 +- 0.0010 d. The host star has a mass of 0.82 +- 0.03 Msun, radius of 0.79 + 0.10 - 0.04 Rsun, effective temperature 5079 +- 88 K, and metallicity [Fe/H] = -0.04 +- 0.08. The planetary companion has a mass of 0.059 +- 0.007 MJ, and radius of 0.565 + 0.072 - 0.032 RJ yielding a mean density of 0.40 +- 0.10 g cm-3. HAT-P-26b is the fourth Neptune-mass transiting planet discovered to date. It has a mass that is comparable to those of Neptune and Uranus, and slightly smaller than those of the other transiting Super-Neptunes, but a radius that is ~65% larger than those of Neptune and Uranus, and also larger than those of the other transiting Super-Neptunes. HAT-P-26b is consistent with theoretical models of an irradiated Neptune-mass planet with a 10 Mearth heavy element core that comprises >~ 50% of its mass with the remainder contained in a significant hydrogen-helium envelope, though the exact composition is uncertain as there are significant differences between various theoretical models at the Neptune-mass regime. The equatorial declination of the star makes it easily accessible to both Northern and Southern ground-based facilities for follow-up observations.

astro-ph.EP↗

arXiv2010

HAT-P-15b: A 10.9-day Extrasolar Planet Transiting a Solar-type Star

We report the discovery of HAT-P-15b, a transiting extrasolar planet in the `period valley', a relatively sparsely-populated period regime of the known extrasolar planets. The host star, GSC 2883-01687, is a G5 dwarf with V=12.16. It has a mass of 1.01+/-0.04 M(Sun), radius of 1.08+/-0.04 R(Sun), effective temperature 5568+/-90 K, and metallicity [Fe/H] = +0.22+/-0.08. The planetary companion orbits the star with a period 10.863502+/-0.000027 days, transit epoch Tc = 2454638.56019+/-0.00048 (BJD), and transit duration 0.2285+/-0.0015 days. It has a mass of 1.946+/-0.066 M(Jup), and radius of 1.072+/-0.043 R(Jup) yielding a mean density of 1.96+/-0.22 g/cm3. At an age of 6.8+/-2.1 Gyr, the planet is H/He-dominated and theoretical models require about 2% (10 M(Earth)) worth of heavy elements to reproduce its measured radius. With an estimated equilibrium temperature of 820 K during transit, and 1000 K at occultation, HAT-P-15b is a potential candidate to study moderately cool planetary atmospheres by transmission and occultation spectroscopy.

astro-ph.EP↗