Rotation modulation of Kepler light curves in mid-A to late-B stars is shown to be present. This is demonstrated by the high correlation of projected rotational velocities with photometric frequencies in 30 stars. The time-frequency diagrams show stochastic variations in all respects similar to those in spotted cool stars. This disposes of any explanation in terms of binary proximity effects. More than half of the sample of stars with effective temperatures in the range of 8300-12000K show rotational modulation, indicating that starspots are the rule rather than the exception among A stars. The periodograms of a subset of these stars show a characteristic pattern in which a broad peak is flanked by a sharp peak at a slightly higher frequency. It is demonstrated that the sharp peak has the same width as the spectral window, indicating a stable period over the duration of the 4-yr Kepler observations. It is speculated that this might be a signature of a reflection effect in a non-transiting planet. These observations suggest that the presence of localized magnetic fields in A and B stars and that current views of radiative stellar envelopes need to be revised.
Stellar X-ray emission plays an important role in the study of exoplanets as a proxy for stellar winds and as a basis for the prediction of extreme ultraviolet (EUV) flux, unavailable for direct measurements, which in their turn are important factors for the mass-loss of planetary atmospheres. Unfortunately, the detection thresholds limit the number of stars with the directly measured X-ray fluxes. At the same time, the known connection between the sunspots and X-ray sources allows using of the starspot variability as an accessible proxy for the stellar X-ray emission. To realize this approach, we analysed the light curves of 1729 main-sequence stars with rotation periods 0.5<P<30d and effective temperatures 3236<Teff<7166K observed by the Kepler mission. It was found that the squared amplitude of the first rotational harmonic of a stellar light curve may be used as a kind of activity index. This averaged index revealed practically the same relation with the Rossby number as that in the case of the X-ray to bolometric luminosity ratio R_x_. As a result, the regressions for stellar X-ray luminosity L_x_(P, T_eff_) and its related EUV analogue L_EUV_ were obtained for the main-sequence stars. It was shown that these regressions allow prediction of average (over the considered stars) values of log(L_x_) and log(L_EUV_) with typical errors of 0.26 and 0.22dex, respectively. This, however, does not include the activity variations in particular stars related to their individual magnetic activity cycles.
We present a grid of forward model transmission spectra, adopting an isothermal temperature-pressure profile, alongside corresponding equilibrium chemical abundances for 117 observationally significant hot exoplanets (equilibrium temperatures of 547-2710K). This model grid has been developed using a 1D radiative-convective-chemical equilibrium model termed ATMO, with up-to-date high-temperature opacities. We present an interpretation of observations of 10 exoplanets, including best-fitting parameters and {chi}^2^ maps. In agreement with previous works, we find a continuum from clear to hazy/cloudy atmospheres for this sample of hot Jupiters. The data for all the 10 planets are consistent with subsolar to solar C/O ratio, 0.005 to 10 times solar metallicity and water rather than methane-dominated infrared spectra. We then explore the range of simulated atmospheric spectra for different exoplanets, based on characteristics such as temperature, metallicity, C/O ratio, haziness and cloudiness. We find a transition value for the metallicity between 10 and 50 times solar, which leads to substantial changes in the transmission spectra. We also find a transition value of C/O ratio, from water to carbon species dominated infrared spectra, as found by previous works, revealing a temperature dependence of this transition point ranging from ~0.56 to ~1-1.3 for equilibrium temperatures from ~900 to ~2600K. We highlight the potential of the spectral features of HCN and C2H2 to constrain the metallicities and C/O ratios of planets, using James Webb Space Telescope (JWST) observations. Finally, our entire grid (~460000 simulations) is publicly available and can be used directly with the JWST simulator PandExo for planning observations.
This catalog was constructed at the Royal Greenwich Observatory in order to enlarge the Gliese (1957) compilation. It contains data on stars nearer than 25 pc that are not included in Gliese's catalog, plus additional information published since 1957 on stars in the Gliese catalog. The machine version contains essentially all information given in Table Ia of the published catalog, plus positional data, and most cross references to other catalogs given in Table IIa. The notes flags in Table Ia are not included because the notes are not machine-readable. Omitted from Table IIa are the finding-chart indicators (Lowell G numbers or notes references) and miscellaneous cross identifications to other names and catalog identifiers. Tables Ib and IIb, containing 21 systems originally included in Gliese's (1957) catalog but for which revised parallaxes have placed them farther than 25 pc are not included in the machine version. Data in the machine version are Gliese number (Newly added stars begin with 9001, but new parallaxes have removed 9419 and added 9849 and 9850; the Sun [first record] has number 0); component identifications for multiple systems; parallax; annual proper motions; radial velocity; (U,V,W) space velocities; box orbit parameters (omega, e, i); spectral type; UBV data; absolute visual magnitude; right ascension (B1950) declination, GCTP (Jenkins 1952, 1963); HD DM, GCRV (Wilson 1953) and other catalog identifiers; BS (= HR) (Hoffleit 1964) numbers; and remarks codes for SB, doubles, variables, etc. Please note that the first entry is for the Sun, and thus it lacks fields such as RA and Dec.
We present the technique and results of a survey of stars within 8pc of the Sun with declinations {delta}>-35{deg} (J2000.00). The survey, designed to find without color bias faint companions, consists of optical coronagraphic images of the 1 field of view centered on each star and infrared direct images with a 32" field of view. The images were obtained through the optical Gunn r and z filters and the infrared J and K filters. The survey achieves sensitivities up to 4 absolute magnitudes fainter than the prototype brown dwarf, Gliese 229B. However, this sensitivity varies with the seeing conditions, the intrinsic brightness of the star observed, and the angular distance from the star. As a result, we tabulate sensitivity limits for each star in the survey. We used the criterion of common proper motion to distinguish companions and to determine their luminosities. In addition to the brown dwarf Gl 229B, we have identified six new stellar companions of the sample stars. Since the survey began, accurate trigonometric parallax measurements for most of the stars have become available. As a result, some of the stars we originally included should no longer be included in the 8pc sample. In addition, the 8pc sample is incomplete at the faint end of the main sequence, complicating our calculation of the binary fraction of brown dwarfs. We assess the sensitivity of the survey to stellar companions and to brown dwarf companions of different masses and ages.
Polarization data are given for stars whose polarizations are mostly interstellar which were observed for various programs with the University of Wisconsin spectropolarimeter (HPOL) during 1989-1994, 1995-2003 and 1995-2004
A list of the 2027 stars that have the largest photometric amplitudes in Hipparcos Photometry shows that the most variables stars are all Miras. The percentage of variable types change as a function of amplitude. This compilation should also be of value to photometrists looking for relatively unstudied, but large amplitude stars.
We present the discovery of four new long-period planets within the HARPS high-precision sample: HD137388b (Msini=0.22M_Jup_), HD204941b (Msini=0.27M_Jup_), HD7199b (Msini=0.29M_Jup_), HD7449b (Msini=1.04M_Jup_). A long-period companion, probably a second planet, is also found orbiting HD7449. Planets around HD137388, HD204941, and HD7199 have rather low eccentricities (less than 0.4) relative to the 0.82 eccentricity of HD7449b. All these planets were discovered even though their hosting stars have clear signs of activity.
The origin of Jupiter-mass planets with orbital periods of only a few days is still uncertain. It is widely believed that these planets formed near the water-ice line of the protoplanetary disk, and subsequently migrated into much smaller orbits. Most of the proposed migration mechanisms can be classified either as disk-driven migration, or as excitation of a very high eccentricity followed by tidal circularization. In the latter scenario, the giant planet that is destined to become a hot Jupiter spends billions of years on a highly eccentric orbit, with apastron near the water-ice line. Eventually, tidal dissipation at periastron shrinks and circularizes the orbit. If this is correct, then it should be especially rare for hot Jupiters to be accompanied by another giant planet interior to the water-ice line. Using the current sample of giant planets discovered with the Doppler technique, we find that hot Jupiters with P_orb_<10d are no more or less likely to have exterior Jupiter-mass companions than longer-period giant planets with P_orb_>=10d. This result holds for exterior companions both inside and outside of the approximate location of the water-ice line. These results are difficult to reconcile with the high-eccentricity migration scenario for hot Jupiter formation.