- ID:
- ivo://CDS.VizieR/J/ApJ/875/29
- Title:
- Spectroscopic analysis of the CKS sample. I.
- Short Name:
- J/ApJ/875/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a quantitative spectroscopic analysis conducted on archival Keck/HIRES high-resolution spectra from the California-Kepler Survey (CKS) sample of transiting planetary host stars identified from the Kepler mission. The spectroscopic analysis was based on a carefully selected set of FeI and FeII lines, resulting in precise values for the stellar parameters of effective temperature (Teff) and surface gravity (logg). Combining the stellar parameters with Gaia DR2 parallaxes and precise distances, we derived both stellar and planetary radii for our sample, with a median internal uncertainty of 2.8% in the stellar radii and 3.7% in the planetary radii. An investigation into the distribution of planetary radii confirmed the bimodal nature of this distribution for the small-radius planets found in previous studies, with peaks at ~1.47+/-0.05 and ~2.72+/-0.10R_{Earth}_ with a gap at ~1.9R_{Earth}_. Previous studies that modeled planetary formation that is dominated by photoevaporation predicted this bimodal radii distribution and the presence of a radius gap, or photoevaporation valley. Our results are in overall agreement with these models, as well as core powered mass-loss models. The high internal precision achieved here in the derived planetary radii clearly reveal the presence of a slope in the photoevaporation valley for the CKS sample, indicating that the position of the radius gap decreases with orbital period; this decrease was fit by a power law of the form R_pl_{propto}P^-0.11^, which is consistent with both photoevaporation and core powered mass-loss models of planet formation, with Earth-like core compositions.
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- ID:
- ivo://CDS.VizieR/J/ApJ/848/11
- Title:
- Spectroscopic and photometric analysis of WDs
- Short Name:
- J/ApJ/848/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed spectroscopic and photometric analysis of 219 DA and DB white dwarfs for which trigonometric parallax measurements are available. Our aim is to compare the physical parameters derived from the spectroscopic and photometric techniques, and then to test the theoretical mass-radius relation for white dwarfs using these results. The agreement between spectroscopic and photometric parameters is found to be excellent, especially for effective temperatures, showing that our model atmospheres and fitting procedures provide an accurate, internally consistent analysis. The values of surface gravity and solid angle obtained, respectively, from spectroscopy and photometry, are combined with parallax measurements in various ways to study the validity of the mass-radius relation from an empirical point of view. After a thorough examination of our results, we find that 73% and 92% of the white dwarfs are consistent within 1{sigma} and 2{sigma} confidence levels, respectively, with the predictions of the mass-radius relation, thus providing strong support to the theory of stellar degeneracy. Our analysis also allows us to identify 15 stars that are better interpreted in terms of unresolved double degenerate binaries. Atmospheric parameters for both components in these binary systems are obtained using a novel approach. We further identify a few white dwarfs that are possibly composed of an iron core rather than a carbon/oxygen core, since they are consistent with Fe-core evolutionary models.
- ID:
- ivo://CDS.VizieR/J/ApJ/770/43
- Title:
- Spectroscopic [Fe/H] of Kepler stars
- Short Name:
- J/ApJ/770/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been shown that F, G, and early K dwarf hosts of Neptune-sized planets are not preferentially metal-rich. However, it is less clear whether the same holds for late K and M dwarf planet hosts. We report metallicities of Kepler targets and candidate transiting planet hosts with effective temperatures below 4500K. We use new metallicity calibrations to determine [Fe/H] from visible and near-infrared spectra. We find that the metallicity distribution of late K and M dwarfs monitored by Kepler is consistent with that of the solar neighborhood. Further, we show that hosts of Earth- to Neptune-sized planets have metallicities consistent with those lacking detected planets and rule out a previously claimed 0.2dex offset between the two distributions at 6{sigma} confidence. We also demonstrate that the metallicities of late K and M dwarfs hosting multiple detected planets are consistent with those lacking detected planets. Our results indicate that multiple terrestrial and Neptune-sized planets can form around late K and M dwarfs with metallicities as low as 0.25 solar. The presence of Neptune-sized planets orbiting such low-metallicity M dwarfs suggests that accreting planets collect most or all of the solids from the disk and that the potential cores of giant planets can readily form around M dwarfs. The paucity of giant planets around M dwarfs compared to solar-type stars must be due to relatively rapid disk evaporation or a slower rate of planet accretion, rather than insufficient solids to form a core.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/397
- Title:
- Spectroscopic study of RGs in the Kepler field
- Short Name:
- J/MNRAS/450/397
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thanks to the recent very high precision photometry of red giants from satellites such as Kepler, precise mass and radius values as well as accurate information of evolutionary stages are already established by asteroseismic approach for a large number of G-K giants. Based on the high-dispersion spectra of selected such 55 red giants in the Kepler field with precisely known seismic parameters (among which parallaxes are available for nine stars), we checked the accuracy of the determination method of stellar parameters previously applied to many red giants by Takeda et al. (2008PASJ...60..781T), since it may be possible to discriminate their complex evolutionary status by using the surface gravity versus mass diagram. We confirmed that our spectroscopic gravity and the seismic gravity satisfactorily agree with each other (to within ~0.1 dex) without any systematic difference. However, the mass values of He-burning red clump giants derived from stellar evolutionary tracks (~2-3 M_{sun}_) were found to be markedly larger by ~50 percent compared to the seismic values (~1-2 M_{sun}_) though such discrepancy is not seen for normal giants in the H-burning phase, which reflects the difficulty of mass determination from intricately overlapping tracks on the luminosity versus effective temperature diagram. This consequence implies that the mass results of many red giants in the clump region determined by Takeda et al. are likely to be significantly overestimated. We also compare our spectroscopically established parameters with recent literature values, and further discuss the prospect of distinguishing the evolutionary status of red giants based on the conventional (i.e. non-seismic) approach.
- ID:
- ivo://CDS.VizieR/J/ApJ/652/681
- Title:
- Spectroscopic subcomponents in multiple systems
- Short Name:
- J/ApJ/652/681
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We propose a methodology for analyzing triple stellar systems that include a visual double star wherein one of the components is a single- or double-lined spectroscopic binary. By using this methodology, we can calculate the most probable values of the spectroscopic binary's inclination, the angular separation between its components, and its stellar masses, and we can even estimate the spectral types. For a few W UMa-type eclipsing binaries, stellar radii are also determined. Moreover, we present new formulae for calculating stellar masses depending on spectral type. In this way we have studied 61 triple systems, five of them W UMatype eclipsing binaries with low-mass subcomponents. In addition, we study nine quadruple systems, applying the same methodology and considering them twice as a triple system.
- ID:
- ivo://CDS.VizieR/J/ApJ/771/107
- Title:
- Spectroscopy of faint KOI stars
- Short Name:
- J/ApJ/771/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar properties are measured for a large set of Kepler mission exoplanet candidate host stars. Most of these stars are fainter than 14th magnitude, in contrast to other spectroscopic follow-up studies. This sample includes many high-priority Earth-sized candidate planets. A set of model spectra are fitted to R~3000 optical spectra of 268 stars to improve estimates of T_eff_, log(g), and [Fe/H] for the dwarfs in the range 4750<=T_eff_<=7200K. These stellar properties are used to find new stellar radii and, in turn, new radius estimates for the candidate planets. The result of improved stellar characteristics is a more accurate representation of this Kepler exoplanet sample and identification of promising candidates for more detailed study. This stellar sample, particularly among stars with T_eff_>~5200K, includes a greater number of relatively evolved stars with larger radii than assumed by the mission on the basis of multi-color broadband photometry. About 26% of the modeled stars require radii to be revised upward by a factor of 1.35 or greater, and modeling of 87% of the stars suggest some increase in radius. The sample presented here also exhibits a change in the incidence of planets larger than 3-4R_{Earth}_ as a function of metallicity. Once [Fe/H] increases to >=-0.05, large planets suddenly appear in the sample while smaller planets are found orbiting stars with a wider range of metallicity.
- ID:
- ivo://CDS.VizieR/J/AJ/160/38
- Title:
- Spitzer variability detections of 79 brown dwarfs
- Short Name:
- J/AJ/160/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer Space Telescope variability monitoring observations of three low-gravity L dwarfs with previous detections of variability in the near-IR: 2MASSJ0045+16, 2MASSJ0501-00, and 2MASSJ1425-36. We detect significant periodic variability in two of our targets, 2MASS J0045+16 and 2MASS J0501-00. We do not detect variability in 2MASS J1425-36. Combining our new rotation periods with rotational velocities, we calculate inclination angles of 22{deg}{+/-}1{deg}, 60_-8_^+13^{deg}, and 52_-13_^+19^{deg} for 2MASSJ0045+16, 2MASSJ0501-00, and 2MASSJ1425-36, respectively. Our three new objects are consistent with the tentative relations between inclination, amplitude, and color anomaly previously reported. Objects with the highest variability amplitudes are inclined equator on, while the maximum observed amplitude decreases as the inclination angle decreases. We also find a correlation between the inclination angle and (J-K)_2MASS_ color anomaly for the sample of objects with measured inclinations. Compiling the entire sample of brown dwarfs with Spitzer variability detections, we find no enhancement in amplitude for young, early-L dwarfs compared to the field dwarf population. We find a possible enhancement in amplitude of low-gravity late-L dwarfs at 4.5{mu}m. We do not find a correlation between amplitude ratio and spectral type for field dwarfs or for the young population. Finally, we compile the rotation periods of a large sample of brown dwarfs with ages 1Myr-1Gyr and compare the rotation rates predicted by evolutionary models assuming angular momentum conservation. We find that the rotation rates of the current sample of brown dwarfs fall within the expected range set by evolutionary models and breakup limits.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/187
- Title:
- Spot parameters on KIC solar-type stars
- Short Name:
- J/ApJ/871/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Active solar-type stars show large quasi-periodic brightness variations caused by stellar rotation with star spots, and the amplitude changes as the spots emerge and decay. The Kepler data are suitable for investigations of the emergence and decay processes of star spots, which are important to understand the underlying stellar dynamo and stellar flares. In this study, we measured the temporal evolution of the star-spot area with Kepler data by tracing the local minima of the light curves. In this analysis, we extracted the temporal evolution of star spots showing clear emergence and decay without being disturbed by stellar differential rotation. We applied this method to 5356 active solar-type stars observed by Kepler and obtained temporal evolution of 56 individual star spots. We calculated the lifetimes and emergence/decay rates of the star spots from the obtained temporal evolution of the spot area. As a result, we found that the lifetimes (T) of star spots range from 10 to 350days when the spot areas (A) are 0.1%-2.3% of the solar hemisphere. We also compared them with sunspot lifetimes and found that the lifetimes of star spots are much shorter than those extrapolated from an empirical relation of sunspots (T{propto}A), while being consistent with other research on star-spot lifetimes. The emergence and decay rates of star spots are typically 5x10^20^Mx/hr (8MSH/hr) with an area of 0.1%-2.3% of the solar hemisphere and mostly consistent with those expected from sunspots, which may indicate the same underlying processes.
- ID:
- ivo://CDS.VizieR/J/AJ/153/214
- Title:
- Star-forming potential in the Perseus complex
- Short Name:
- J/AJ/153/214
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our investigation of the star-forming potential in the Perseus star-forming complex. We build on previous starless core, protostellar core, and young stellar object (YSO) catalogs from Spitzer (3.6-70 {mu}m), Herschel (70-500 {mu}m), and SCUBA (850 {mu}m) observations in the literature. We place the cores and YSOs within seven star-forming clumps based on column densities greater than 5x10^21^/cm^2^. We calculate the mean density and free-fall time for 69 starless cores as ~5.55x10^-19^ g/cm^3^ and ~0.1 Myr, respectively, and we estimate the star formation rate for the near future as ~150 M_{sun}_/Myr. According to Bonnor-Ebert stability analysis, we find that majority of starless cores in Perseus are unstable. Broadly, these cores can collapse to form the next generation of stars. We found a relation between starless cores and YSOs, where the numbers of young protostars (Class 0 + Class I) are similar to the numbers of starless cores. This similarity, which shows a one-to-one relation, suggests that these starless cores may form the next generation of stars with approximately the same formation rate as the current generation, as identified by the Class 0 and Class I protostars. It follows that if such a relation between starless cores and any YSO stage exists, the SFR values of these two populations must be nearly constant. In brief, we propose that this one-to-one relation is an important factor in better understanding the star formation process within a cloud.
- ID:
- ivo://CDS.VizieR/J/AJ/155/161
- Title:
- Stars nearby Robo-AO Kepler planetary candidates
- Short Name:
- J/AJ/155/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the overall statistical results from the Robo-AO Kepler planetary candidate survey, comprising of 3857 high-angular resolution observations of planetary candidate systems with Robo-AO, an automated laser adaptive optics system. These observations reveal previously unknown nearby stars blended with the planetary candidate host stars that alter the derived planetary radii or may be the source of an astrophysical false positive transit signal. In the first three papers in the survey, we detected 440 nearby stars around 3313 planetary candidate host stars. In this paper, we present observations of 532 planetary candidate host stars, detecting 94 companions around 88 stars; 84 of these companions have not previously been observed in high resolution. We also report 50 more-widely separated companions near 715 targets previously observed by Robo-AO. We derive corrected planetary radius estimates for the 814 planetary candidates in systems with a detected nearby star. If planetary candidates are equally likely to orbit the primary or secondary star, the radius estimates for planetary candidates in systems with likely bound nearby stars increase by a factor of 1.54, on average. We find that 35 previously believed rocky planet candidates are likely not rocky due to the presence of nearby stars. From the combined data sets from the complete Robo-AO KOI survey, we find that 14.5+/-0.5% of planetary candidate hosts have a nearby star with 4", while 1.2% have two nearby stars, and 0.08% have three. We find that 16% of Earth-sized, 13% of Neptune-sized, 14% of Saturn-sized, and 19% of Jupiter-sized planet candidates have detected nearby stars.
