Kathryn M. G. Peek

A New Planet around an M Dwarf: Revealing a Correlation between Exoplanets and Stellar Mass*

We report precise Doppler measurements of GJ 317 (M3.5 V) that reveal the presence of a planet with a minimum mass M_P sin i = 1.2 M_(Jup) in an eccentric, 692.9 day orbit. GJ 317 is only the third M dwarf with a Doppler-detected Jovian planet. The residuals to a single-Keplerian fit show evidence of a possible second orbital companion. The inclusion of a second Jupiter-mass planet (P ≈ 2700 days, M_P sin i = 0.83 M_(Jup)) decreases √X_v^2 from 2.02 to 1.23, and reduces the rms from 12.5 to 6.32 m s^(-1). A false-alarm test yields a 1.1% probability that the curvature in the residuals of the single-planet fit is due to random fluctuations, lending additional credibility to the two-planet model. However, our data only marginally constrain a two-planet fit, and further monitoring is necessary to fully characterize the properties of the second companion. To study the effect of stellar mass on giant planet occurrence, we measure the fraction of stars with planets in three mass bins comprised of our samples of M Dwarfs, solar-mass stars, and intermediate-mass subgiants. We find a positive correlation between stellar mass and the occurrence rate of Jovian planets within 2.5 AU. Low-mass K and M stars have a 1.8% ± 1.0% planet occurrence rate compared to 4.2% ± 0.7% for solar-mass stars and 8.9% ± 2.9% for the higher mass subgiants. This result indicates that the former F- and A-type stars with M_* ≥ 1.3 M_☉ in our sample are nearly 5 times more likely than the M dwarfs to harbor a giant planet. Our analysis shows that the correlation between Jovian planet occurrence and stellar mass exists even after correcting for the effects of stellar metallicity.

Five Planets Orbiting 55 Cancri

Wereport18yearsof Dopplershiftmeasurementsof anearbystar,55Cancri,thatexhibitsstrongevidenceforfive orbiting planets. The four previously reported planets are strongly confirmed here. Afifth planet is presented, with an apparent orbital period of 260 days, placing it 0.78 AU from the star in the large empty zone between two other planets. The velocity wobble amplitude of 4.9 m s � 1 implies a minimum planet massM sini ¼ 45:7 M� . The orbital eccentricity is consistent with a circular orbit, but modest eccentricity solutions give similar � 2 fits. All five planets resideinlow-eccentricityorbits,fourhavingeccentricitiesunder0.1.Theoutermostplanetorbits5.8AUfromthestar andhasaminimummassM sini ¼ 3:8 MJup,makingitmoremassivethantheinnerfourplanetscombined.Itsorbital distance is the largest for an exoplanet with a well-defined orbit. The innermost planet has a semimajor axis of only 0.038 AU and has a minimum mass, M sini, of only 10.8 M� , making it one of the lowest mass exoplanets known. The five known planets within 6 AU define a minimum-mass protoplanetary nebula to compare with the classical minimum-masssolarnebula.NumericalN-bodysimulationsshowthissystemoffiveplanetstobedynamicallystable and show that the planets with periods of 14.65 and 44.3 days are not in a mean motion resonance. Millimagnitude photometry during 11 years reveals no brightness variations at any of the radial velocity periods, providing support for their interpretation as planetary. Subject headingg planetary systems — stars: individual (55 Cancri, HD 75732, � 1 Cancri)

The California Planet Survey. I. Four New Giant Exoplanets

We present precise Doppler measurements of four stars obtained during the past decade at Keck Observatory by the California Planet Survey (CPS). These stars, namely, HD 34445, HD 126614, HD 13931, and Gl 179, all show evidence for a single planet in Keplerian motion. We also present Doppler measurements from the Hobby-Eberly Telescope (HET) for two of the stars, HD 34445 and Gl 179, that confirm the Keck detections and significantly refine the orbital parameters. These planets add to the statistical properties of giant planets orbiting near or beyond the ice line, and merit follow-up by astrometry, imaging, and space-borne spectroscopy. Their orbital parameters span wide ranges of planetary minimum mass (M sin i = 0.38-1.9 M_(Jup)), orbital period (P = 2.87-11.5 yr), semimajor axis (a = 2.1-5.2 AU), and eccentricity (e = 0.02-0.41). HD 34445 b (P = 2.87 yr, M sin i = 0.79 M_(Jup), e = 0.27) is a massive planet orbiting an old, G-type star. We announce a planet, HD 126614 Ab, and an M dwarf, HD 126614 B, orbiting the metal-rich star HD 126614 (which we now refer to as HD 126614 A). The planet, HD 126614 Ab, has minimum mass M sin i = 0.38 M_(Jup) and orbits the stellar primary with period P = 3.41 yr and orbital separation a = 2.3 AU. The faint M dwarf companion, HD 126614 B, is separated from the stellar primary by 489 mas (33 AU) and was discovered with direct observations using adaptive optics and the PHARO camera at Palomar Observatory. The stellar primary in this new system, HD 126614 A, has the highest measured metallicity ([Fe/H] = +0.56) of any known planet-bearing star. HD 13931 b (P = 11.5 yr, M sin i = 1.88 M_(Jup), e = 0.02) is a Jupiter analog orbiting a near solar twin. Gl 179 b (P = 6.3 yr, M sin i = 0.82 M Jup, e = 0.21) is a massive planet orbiting a faint M dwarf. The high metallicity of Gl 179 is consistent with the planet-metallicity correlation among M dwarfs, as documented recently by Johnson & Apps.

RETIRED A STARS AND THEIR COMPANIONS. III. COMPARING THE MASS-PERIOD DISTRIBUTIONS OF PLANETS AROUND A-TYPE STARS AND SUN-LIKE STARS

We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 ≾ M_*/M_☉ ≾ 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov-Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26^(+9)_(–8)%, which is significantly higher than the 5%-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} M_(Jup) within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around IM stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN ∝ M^α P^β dlnMdlnP, the observed planet frequency, and the detection limits we derived. We find that the values of α and β for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4σ level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets.

VARIABLE SODIUM ABSORPTION IN A LOW-EXTINCTION TYPE Ia SUPERNOVA*, **

Recent observations have revealed that some Type Ia supernovae exhibit narrow, time-variable Na I D absorption features. The origin of the absorbing material is controversial, but it may suggest the presence of circumstellar gas in the progenitor system prior to the explosion, with significant implications for the nature of the supernova (SN) progenitors. We present the third detection of such variable absorption, based on six epochs of high-resolution spectroscopy of the Type Ia supernova SN 2007le from the Keck I Telescope and the Hobby-Eberly Telescope. The data span a time frame of approximately three months, from 5 days before maximum light to 90 days after maximum. We find that one component of the NaID absorption lines strengthened significantly with time, indicating a total column density increase of ~2.5 × 10^(12) cm^(–2). The data limit the typical timescale for the variability to be more than 2 days but less than 10 days. The changes appear to be most prominent after maximum light rather than at earlier times when the ultraviolet flux from the SN peaks. As with SN 2006X, we detect no change in the Ca II H and K absorption lines over the same time period, rendering line-of-sight effects improbable and suggesting a circumstellar origin for the absorbing material. Unlike the previous two supernovae exhibiting variable absorption, SN 2007le is not highly reddened (E_(B – V) = 0.27 mag), also pointing toward circumstellar rather than interstellar absorption. Photoionization calculations show that the data are consistent with a dense (10^7 cm^(–3)) cloud or clouds of gas located ~0.1 pc (3 × 10^(17) cm) from the explosion. These results broadly support the single-degenerate scenario previously proposed to explain the variable absorption, with mass loss from a nondegenerate companion star responsible for providing the circumstellar gas. We also present possible evidence for narrow Hα emission associated with the SN, which will require deep imaging and spectroscopy at late times to confirm.

THE LOCAL LEO COLD CLOUD AND NEW LIMITS ON A LOCAL HOT BUBBLE

We present a multi-wavelength study of the local Leo cold cloud (LLCC), a very nearby, very cold cloud in the interstellar medium (ISM). Through stellar absorption studies we find that the LLCC is between 11.3 pc and 24.3 pc away, making it the closest known cold neutral medium cloud and well within the boundaries of the local cavity. Observations of the cloud in the 21 cm H I line reveal that the LLCC is very cold, with temperatures ranging from 15 K to 30 K, and is best fit with a model composed of two colliding components. The cloud has associated 100 μm thermal dust emission, pointing to a somewhat low dust-to-gas ratio of 48 ×10–22 MJy sr–1 cm2. We find that the LLCC is too far away to be generated by the collision among the nearby complex of local interstellar clouds but that the small relative velocities indicate that the LLCC is somehow related to these clouds. We use the LLCC to conduct a shadowing experiment in 1/4 keV X-rays, allowing us to differentiate between different possible origins for the observed soft X-ray background (SXRB). We find that a local hot bubble model alone cannot account for the low-latitude SXRB, but that isotropic emission from solar wind charge exchange (SWCX) does reproduce our data. In a combined local hot bubble and SWCX scenario, we rule out emission from a local hot bubble with an 1/4 keV emissivity greater than 1.1 Snowdens pc–1 at 3σ, four times lower than previous estimates. This result dramatically changes our perspective on our local ISM.

Old, Rich, and Eccentric: Two Jovian Planets Orbiting Evolved Metal-Rich Stars

We present radial velocity measurements of two stars observed as part of the Lick Subgiants Planet Search and the Keck N2K survey. Variations in the radial velocities of both stars reveal the presence of Jupiter-mass exoplanets in highly eccentric orbits. HD 16175 is a G0 subgiant from the Lick Subgiants Planet Search, orbited by a planet having a minimum mass of 4.4 MJup, in an eccentric (e = 0.59), 2.71 yr orbit. HD 96167 is a G5 subgiant from the N2K (“Next 2000”) program at Keck Observatory, orbited by a planet having a minimum mass of 0.68 MJup, in an eccentric (e = 0.71), 1.366 yr orbit. Both stars are relatively massive (M⋆ = 1.3 M⊙) and are very metal rich ([Fe/H] > +0.3). We describe our methods for measuring the stars’ radial velocity variations and photometric stability.

A Substellar Companion in a 1.3 yr Nearly-circular Orbit of HD 16760

We report the detection of a substellar companion orbiting the G5 dwarf HD 16760 from the N2K sample. Precise Doppler measurements of the star from Subaru and Keck revealed a Keplerian velocity variation with a period of 466.47 ± 0.35 d, a semiamplitude of 407.71 ± 0.84 m s^(–1), and an eccentricity of 0.084 ± 0.003. Adopting a stellar mass of 0.78 ± 0.05 M_☉, we obtain a minimum mass for the companion of 13.13 ± 0.56 M_(JUP), which is close to the planet/brown-dwarf transition, and the semimajor axis of 1.084 ± 0.023 AU. The nearly circular orbit despite the large mass and intermediate orbital period makes this companion unique among known substellar companions.

A New Technique for Determining Europium Abundances in Solar-Metallicity Stars*

We present a new technique for measuring the abundance of europium, a representative r-process element, in solar-metallicity stars. Our algorithm compares LTE synthetic spectra with high-resolution observational spectra using a χ 2 -minimization routine. The analysis is fully automated, and therefore allows consistent measure- ment of blended lines even across very large stellar samples. We compare our results with literature europium abundance measurements and find them to be consistent; we also find that our method generates smaller errors. Every atom heavier than lithium has been processed by stars. Elements of the α-process, iron peak, and r-process have dif- ferent formation sites, and therefore, understanding the dis- tribution of these elements in nearby stars can lead to a better understanding of the Galaxys chemical enrichment history. The r-process site is the least well understood. Europium (Eu) is our choice for an r-process investigation for two reasons: 96% of Galactic europium is formed through the r-process (Burris et al. 2000), and it has several strong lines in the visible portion of the electromagnetic spectrum. In order to provide insight into the Galactic enrichment history, however, europium measurements

The Detection of a Large‐mass Planet Around a K0 IV Subgiant With an Almost‐circular Orbit

We report the detection of a new large‐mass planet orbiting around a K0 IV(V = 8.26) star which has a minimum mass M_p sin i = 10.70 ± 0.50 M_(Jup) in a 696.0 ± 2.6‐day orbit. It was detected in precise radial velocity (RV) measurements from Subaru and Keck. The derived orbital parameters, based on a χ^2 which minimized by Downhill Simplex algorithm, suggests that these radial velocity variations are consistent with an almost circular planetary orbit and a Mars‐like semimajor axis (e ∼ 0.0, a  =  1.70 ± 0.03 AU). Extra‐solar planets that have several times the mass of Jupiter orbiting in periods of hundreds or thousands of days, with very low eccentricities( e< 0.1), are rare discoveries. Our detection presents a new sample of these circular orbit massive planets.