- ID:
- ivo://CDS.VizieR/J/AJ/155/79
- Title:
- RV & light curves data for 4 G-type dwarf stars
- Short Name:
- J/AJ/155/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of four close-in transiting exoplanets (HATS-50b through HATS-53b), discovered using the HATSouth three-continent network of homogeneous and automated telescopes. These new exoplanets belong to the class of hot Jupiters and orbit G-type dwarf stars, with brightness in the range V=12.5-14.0 mag. While HATS-53 has many physical characteristics similar to the Sun, the other three stars appear to be metal-rich ([Fe/H]=0.2-0.3), larger, and more massive. Three of the new exoplanets, namely HATS-50b, HATS-51b, and HATS-53b, have low density (HATS-50b: 0.39+/-0.10 M_J_, 1.130+/-0.075 R_J_; HATS-51b: 0.768+/-0.045 M_J_, 1.41+/-0.19 R_J_; HATS-53b: 0.595+/-0.089 M_J_, 1.340+/-0.056 R_J_) and similar orbital periods (3.8297 days, 3.3489 days, 3.8538 days, respectively). Instead, HATS-52b is more dense (mass 2.24+/-0.15 M_J_ and radius 1.382+/-0.086 R_J_) and has a shorter orbital period (1.3667 days). It also receives an intensive radiation from its parent star and, consequently, presents a high equilibrium temperature (T_eq_=1834+/-73 K). HATS-50 shows a marginal additional transit feature consistent with an ultra-short-period hot super Neptune (upper mass limit 0.16 M_J_), which will be able to be confirmed with TESS photometry.
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- ID:
- ivo://CDS.VizieR/J/AJ/158/165
- Title:
- RV observations & activity indicators for Kepler-538b
- Short Name:
- J/AJ/158/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V=11.27) with M_*_=0.892_-0.035_^+0.051^ M_{sun}_ and R_*_=0.8717_-0.0061_^+0.0064^ R_{sun}_. Kepler-538b is a 2.215_-0.034_^+0.040^ R_{Earth}_ sub-Neptune with a period of P=81.73778+/-0.00013 days. It is the only known planet in the system. We collected radial velocity (RV) observations with the High Resolution Echelle Spectrometer (HIRES) on Keck I and High Accuracy Radial velocity Planet Searcher in North hemisphere (HARPS-N) on the Telescopio Nazionale Galileo (TNG). We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross-correlation function FWHM observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of K=1.68_-0.38_^+0.39^ m/s and a planet mass of M_p_=10.6_-2.4_^+2.5^ M_{Earth}_. Kepler-538b is the smallest planet beyond P=50 days with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/88
- Title:
- Short-duration stellar flares from GALEX & Kepler
- Short Name:
- J/ApJ/883/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a population of short-duration near-ultraviolet (NUV) flares in stars observed by the Kepler and Galaxy Evolution Explorer (GALEX) missions. We analyzed the NUV light curves of 34276 stars observed from 2009 to 2013 by both the GALEX (NUV) and Kepler (optical) space missions with the eventual goal of investigating multiwavelength flares. From the GALEX data, we constructed light curves with a 10s cadence, and we ultimately detected 1904 short-duration flares on 1021 stars. The vast majority (94.5%) of these flares have durations less than 5 minutes, with flare flux enhancements above the quiescent flux level ranging from 1.5 to 1700. The flaring stars are primarily solar-like, with Teff ranging from 3000 to 11000K and radii between 0.5 and 15R_{sun}_. This set of flaring stars is almost entirely distinct from that of previous flare surveys of Kepler data and indicates a previously undetected collection of small flares contained within the Kepler sample. The range in flare energies spans 1.8x10^32^-8.9x10^37^erg, with associated relative errors spanning 2%-87%. The flare frequency distribution by energy follows a power law with index {alpha}=1.72+/-0.05, consistent with results of other solar and stellar flare studies at a range of wavelengths. This supports the idea that the NUV flares we observed are governed by the same physical processes present in solar and optical flares. The relationship between flare duration and associated flare energy extends results found for solar and stellar white-light flares, and suggests that these flares originate in regions with magnetic field strengths of several hundred Gauss, and length scales of the order of 10^10^cm.
- ID:
- ivo://CDS.VizieR/J/ApJ/812/12
- Title:
- S-index and Stroemgren LC of HD30495
- Short Name:
- J/ApJ/812/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A growing body of evidence suggests that multiple dynamo mechanisms can drive magnetic variability on different timescales, not only in the Sun but also in other stars. Many solar activity proxies exhibit a quasi-biennial (~2yr) variation, which is superimposed upon the dominant 11 year cycle. A well-characterized stellar sample suggests at least two different relationships between rotation period and cycle period, with some stars exhibiting long and short cycles simultaneously. Within this sample, the solar cycle periods are typical of a more rapidly rotating star, implying that the Sun might be in a transitional state or that it has an unusual evolutionary history. In this work, we present new and archival observations of dual magnetic cycles in the young solar analog HD 30495, a ~1Gyr old G1.5V star with a rotation period near 11 days. This star falls squarely on the relationships established by the broader stellar sample, with short-period variations at ~1.7yr and a long cycle of ~12yr. We measure three individual long-period cycles and find durations ranging from 9.6 to 15.5yr. We find the short-term variability to be intermittent, but present throughout the majority of the time series, though its occurrence and amplitude are uncorrelated with the longer cycle. These essentially solar-like variations occur in a Sun-like star with more rapid rotation, though surface differential rotation measurements leave open the possibility of a solar equivalence.
- ID:
- ivo://CDS.VizieR/J/ApJ/790/L23
- Title:
- Solar analogs and twins rotation by Kepler
- Short Name:
- J/ApJ/790/L23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new sample of solar analogs and twin candidates has been constructed and studied, paying particular attention to their light curves from NASA's Kepler mission. This Letter aims to assess their evolutionary status, derive their rotation and ages, and identify those which are solar analogs or solar twin candidates. We separate out the subgiants that compose a large fraction of the asteroseismic sample, and which show an increase in the average rotation period as the stars ascend the subgiant branch. The rotation periods of the dwarfs, ranging from 6 to 30 days and averaging 19 days, allow us to assess their individual evolutionary states on the main sequence and to derive their ages using gyrochronology. These ages are found to be in agreement with a correlation coefficient of r = 0.79 with independent asteroseismic ages, where available. As a result of this investigation, we are able to identify 34 stars as solar analogs and 22 of them as solar twin candidates.
- ID:
- ivo://CDS.VizieR/J/AZh/88/1217
- Title:
- Solar-like activity of low-mass stars
- Short Name:
- J/AZh/88/1217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An analysis of data on chromospheric activity obtained in the framework of exoplanet-search programs is presented. Observations of 1334 stars showing that the chromospheric activity of the Sun is clearly higher than for the vast majority of stars in the solar vicinity are used. A comparison of chromospheric and coronal activity led to the identification of a significant group of stars with a low level of chromospheric activity, whose coronal radiation spans wide ranges.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A175
- Title:
- Solar system analogs with HARPS
- Short Name:
- J/A+A/615/A175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The assessment of the frequency of planetary systems reproducing the solar system's architecture is still an open problem in exoplanetary science. Detailed study of multiplicity and architecture is generally hampered by limitations in quality, temporal extension and observing strategy, causing difficulties in detecting low-mass inner planets in the presence of outer giant planets. We present the results of high-cadence and high-precision HARPS observations on 20 solar-type stars known to host a single long-period giant planet in order to search for additional inner companions and estimate the occurence rate f_p_ of scaled solar system analogues - in other words, systems featuring lower-mass inner planets in the presence of long-period giant planets. We carried out combined fits of our HARPS data with literature radial velocities using differential evolution MCMC to refine the literature orbital solutions and search for additional inner planets. We then derived the survey detection limits to provide preliminary estimates of f_p_. We generally find better constrained orbital parameters for the known planets than those found in the literature; significant updates can be especially appreciated on half of the selected planetary systems. While no additional inner planet is detected, we find evidence for previously unreported long-period massive companions in systems HD 50499 and HD 73267. We finally estimate the frequency of inner low mass (10-30M_{earth}_) planets in the presence of outer giant planets as f_p_<9.84% for P<150-days. Our preliminary estimate of f_p_ is significantly lower than the literature values for similarly defined mass and period ranges; the lack of inner candidate planets found in our sample can also be seen as evidence corroborating the inwards-migration formation model for super-Earths and mini-Neptunes. Our results also underline the need for high-cadence and high-precision followup observations as the key to precisely determine the occurence of solar system analogues.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A73
- Title:
- Solar Twins age-chromospheric activity
- Short Name:
- J/A+A/619/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1-2Gyr that is followed by a relatively inactive constant phase. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. We measured the CaII H and K activity indices using 9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale (S_MW_), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of Te, and then computed an improved bolometric flux normalized activity index logR'_HK_(Teff) for the entire sample. New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using logR'_HK_(Teff). We measured an average solar activity of S_MW_=0.1712+/-0.0017 during solar magnetic cycles 23-24 covered by HARPS observations, and we also inferred an average of S_MW_=0.1694+/-0.0025 for cycles 10-24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6-7Gyr, in agreement with previous works using open clusters and field stars with precise ages. Our research confirms that CaII H& K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6-7Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations eects. The Sun seems to have a normal activity level and variability for its age.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A131
- Title:
- Solar twins in the ELODIE archive
- Short Name:
- J/A+A/587/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A large dataset of ~2800 spectra extracted from the ELODIE archive was analysed in order to find solar twins. Stellar spectra closely resembling the spectrum of the Sun were selected by applying a purely differential method, directly on the fluxes. As solar reference, 18 spectra of asteroids, of the Moon, and of the blue sky were used. Atmospheric parameters and differential abundances of eight chemical elements were determined for the solar twin candidates after a careful selection of appropriate lines. The Li feature of the targets was investigated and additional information on absolute magnitude and age was gathered from the literature. HIP076114 (HD138573) is our best twin candidate; it looks exactly like the Sun in all these properties.
- ID:
- ivo://CDS.VizieR/J/AJ/151/89
- Title:
- Spectroscopy and photometry of HATS-17
- Short Name:
- J/AJ/151/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of HATS-17b, the first transiting warm Jupiter of the HATSouth network. HATS-17b transits its bright (V=12.4) G-type (M_{star}_=1.131+/-0.030M_{sun}_, R_{star}_=1.090_-0.046_^+0.070^) metal-rich ([Fe/H]=+0.3dex) host star in a circular orbit with a period of P=16.2546days. HATS-17b has a very compact radius of 0.777+/-0.056R_J_ given its Jupiter-like mass of 1.338+/-0.065M_J_. Up to 50% of the mass of HATS-17b may be composed of heavy elements in order to explain its high density with current models of planetary structure. HATS-17b is the longest period transiting planet discovered to date by a ground-based photometric survey, and is one of the brightest transiting warm Jupiter systems known. The brightness of HATS-17 will allow detailed follow-up observations to characterize the orbital geometry of the system and the atmosphere of the planet.
