- ID:
- ivo://CDS.VizieR/J/AJ/162/11
- Title:
- EDEN project: Flare activity of nearby M-dwarf Wolf 359
- Short Name:
- J/AJ/162/11
- Date:
- 16 Mar 2022 00:09:17
- Publisher:
- CDS
- Description:
- We report the flare activity of Wolf359, the fifth closest star to the Sun and a candidate exoplanet-hosting M-dwarf. The star was a target of the Kepler/K2 mission and was observed by the EDEN project, a global network of 1-2m class telescopes for detection and characterization of rocky exoplanets in the habitable zones of late M-dwarfs within 50 light year from the solar system. In the combination of the archived K2 data and our EDEN observations, a total of 872 flares have been detected, 861 with the K2 (860 in the short-cadence and 18 in the long-cadence data, with 17 long-cadence events having short-cadence counterparts) and 11 with EDEN. Wolf 359 has relatively strong flare activity even among flaring M-dwarfs, in terms of the flare activity indicator (FA) defined as the integrated flare energy relative to the total stellar bolometric energy, where FA={sum}E_f_/{int}L_bol_dt~8.93x10^-5^ for the long-cadence flares, whereas for K2 short cadence and EDEN flares, the FA values are somewhat larger, FA~6.67 x 10^-4^ and FA~5.25x10^-4^, respectively. Such a level of activity, in accordance with the rotation period (P_rot_), suggests the star to be in the saturation phase. The size of the starspots is estimated to be at least 1.87%{+/-}0.59% of the projected disk area of Wolf359. We find no correlation of FA with the stellar rotational phase. Our analysis indicates a flare frequency distribution in a power-law form of dN/dE{prop}E^-{alpha}^ with {alpha}=2.13{+/-}0.14, equivalent to an occurrence rate of flares E_f_>~10^31^erg about once per day and of superflares with E_f_>~10^33^erg approximately 10 times per year. These superflares may impact the habitability of system in multiple ways, the details of which are topics for future investigations.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/411/559
- Title:
- Effective temperature for 181 F-K dwarfs
- Short Name:
- J/A+A/411/559
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Line depth ratios measured on high resolution (R=42000), high S/N echelle spectra are used for the determination of precise effective temperatures of 181 F, G, K main Sequence stars with about solar metallicity (-0.5<[Fe/H]<+0.5). A set of 105 relations is obtained which rely Teff on ratios of the strengths of lines with high and low excitation potentials, calibrated against previously published precise (1%) temperature estimates. The application range of the calibrations is 4000-6150K (F8V-K7V). The internal error of a single calibration is less than 100K, while the combination of all calibrations for a spectrum of S/N=100 reduces uncertainty to only 5-10K, and for S/N=200 or higher to better than 5K. The zero point of the temperature scale is directly defined from reflection spectra of the Sun with an uncertainty about 1K. The application of this method to investigation of the planet host stars properties is discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/590/A50
- Title:
- eMSTOs in low mass clusters
- Short Name:
- J/A+A/590/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an imaging analysis of four low mass stellar clusters (<~5000M_{sun}_) in the outer regions of the LMC in order to shed light on the extended main sequence turn-off (eMSTO) phenomenon observed in high mass clusters. The four clusters have ages between 1-2Gyr and two of them appear to host eMTSOs. The discovery of eMSTOs in such low mass clusters - more than 5 times less massive than the eMSTO clusters previously studied - suggests that mass is not the controlling factor in whether clusters host eMSTOs. Additionally, the narrow extent of the eMSTO in the two older clusters (~2Gyr) is in agreement with predictions of the stellar rotation scenario, as lower mass stars are expected to be magnetically braked, meaning that their colour magnitude diagrams should be better reproduced by canonical simple stellar populations. We also performed a structural analysis on all the clusters and found that a large core radius is not a requisite for a cluster to exhibit an eMSTO.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A137
- Title:
- Evolution of Li in FGK dwarf stars
- Short Name:
- J/A+A/654/A137
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We investigate two topics regarding solar mass FGK-type stars, the lithium rotation connection (LRC) and the existence of the "lithium desert". We determine the minimum critical rotation velocity (vsini) related with the LRC separating slow from rapid stellar rotators, as being 5km/s. This value also split different stellar properties. For the first time we explore the behaviour of the LRC for some stellar associations with ages between 45Myr and 120Myr. This allows us to study the LRC age dependence at the beginning of the general spin down stage for low mass stars, which starts at ~30-40Myr. We find that each stellar group presents a characteristic minimum lithium (Li) depletion connected to a specific large rotation velocity and that this minimum changes with age. For instance, this minimum changes from ~50km/s to less than 20km/s in 200Myr. Regarding the lithium desert, it was described as a limited region in the A(Li)-Teff map containing no stars. Using Teff from Gaia DR2 we detect 30 stars inside and/or near the same box defined originally as the Li desert. Due to their intrinsic Teff errors some of these stars may be inside or outside the box, implying a large probability that the box contains several stars. Considering this last fact the "lithium desert" appears to be more a statistical distribution fluctuation than a real problem.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A71
- Title:
- Evolution of rotating very massive LC stars
- Short Name:
- J/A+A/573/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With growing evidence for the existence of very massive stars at subsolar metallicity, there is an increased need for corresponding stellar evolution models. We present a dense model grid with a tailored input chemical composition appropriate for the Large Magellanic Cloud (LMC).
- ID:
- ivo://CDS.VizieR/J/AJ/159/211
- Title:
- Exoplanet parameters from Kepler and K2
- Short Name:
- J/AJ/159/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present calculations of the occurrence rate of small close-in planets around low-mass dwarf stars using the known planet populations from the Kepler and K2 missions. Applying completeness corrections clearly reveals the radius valley in the maximum a posteriori occurrence rates as a function of orbital separation and planet radius. We measure the slope of the valley to be r_p,valley_{prop}F^-0.060{+/-}0.025^, which bears the opposite sign from that measured around Sun-like stars, thus suggesting that thermally driven atmospheric mass loss may not dominate the evolution of planets in the low stellar mass regime or that we are witnessing the emergence of a separate channel of planet formation. The latter notion is supported by the relative occurrence of rocky to non-rocky planets increasing from 0.5{+/-}0.1 around mid-K dwarfs to 8.5{+/-}4.6 around mid-M dwarfs. Furthermore, the center of the radius valley at 1.54{+/-}0.16R{earth} is shown to shift to smaller sizes with decreasing stellar mass, in agreement with physical models of photoevaporation, core-powered mass loss, and gas-poor formation. Although current measurements are insufficient to robustly identify the dominant formation pathway of the radius valley, such inferences may be obtained by the Transiting Exoplanet Survey Satellite with O(85000) mid-to-late M dwarfs observed with 2minutes cadence. The measurements presented herein also precisely designate the subset of planetary orbital periods and radii that should be targeted in radial velocity surveys to resolve the rocky to non-rocky transition around low-mass stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/693/L81
- Title:
- Extinction in star-forming regions
- Short Name:
- J/ApJ/693/L81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using Spitzer Infrared Spectrograph observations of G0-M4III stars behind dark clouds, I construct 5-20um empirical extinction curves for 0.3<=A_K_<7, which is equivalent to A_V_ between ~3 and 50. For A_K_<1, the curve appears similar to the Mathis diffuse interstellar medium extinction curve, but with a greater degree of extinction. For A_K_>1, the curve exhibits lower contrast between the silicate and absorption continuum, develops ice absorption, and lies closer to the Weingartner and Draine R_V_=5.5 Case B curve, a result which is consistent with that of Flaherty et al. (2007ApJ...663.1069F) and Chiar et al. (2007ApJ...666L..73C). Recently, work using Spitzer Infrared Array Camera data by Chapman et al. independently reaches a similar conclusion that the shape of the extinction curve changes as a function of increasing A_K_. By calculating the optical depths of the 9.7um silicate and 6.0, 6.8, and 15.2um ice features, I determine that a process involving ice is responsible for the changing shape of the extinction curve and speculate that this process is a coagulation of ice-mantled grains rather than ice-mantled grains alone.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A55
- Title:
- Extrasolar planets. Radial velocities of 5 stars
- Short Name:
- J/A+A/545/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial-velocity measurements obtained in one of a number of programs underway to search for extrasolar planets with the spectrograph SOPHIE at the 1.93-m telescope of the Haute-Provence Observatory. Targets were selected from catalogs observed with ELODIE, which had been mounted previously at the telescope, in order to detect long-period planets with an extended database close to 15 years.
- ID:
- ivo://CDS.VizieR/J/MNRAS/475/2480
- Title:
- Extremely-low mass white dwarf star
- Short Name:
- J/MNRAS/475/2480
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The so-called sdA stars are defined by having H-rich spectra and surface gravities similar to hot subdwarf stars, but effective temperature below the zero-age horizontal branch. Their evolutionary history is an enigma: their surface gravity is too high for main-sequence stars, but too low for single evolution white dwarfs. They are most likely byproducts of binary evolution, including blue-stragglers, extremely-low mass white dwarf stars (ELMs) and their precursors (pre-ELMs). A small number of ELMs with similar properties to sdAs is known. Other possibilities include metal-poor A/F dwarfs, second generation stars, or even stars accreted from dwarf galaxies. In this work, we analyse colours, proper motions, and spacial velocities of a sample of sdAs from the Sloan Digital Sky Survey to assess their nature and evolutionary origin. We define a probability of belonging to the main sequence and a probability of being a (pre-)ELM based on these properties. We find that 7 per cent of the sdAs are more likely to be (pre-)ELMs than main-sequence stars. However, the spacial velocity distribution suggests that over 35 per cent of them cannot be explained as single metal-poor A/F stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/358/13
- Title:
- Faint dwarfs in NGC 2547
- Short Name:
- J/MNRAS/358/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Intermediate resolution spectroscopy from the European Southern Observatory Very Large Telescope is analysed for 63 photometrically selected low-mass (0.08-0.30M_{sun}_) candidates of the open cluster NGC 2547. We have confirmed membership for most of these stars using radial velocities, and found that lithium remains undepleted for cluster stars with I>17.54+/-0.14 and Ks>14.86+/-0.12. From these results, several pre-main-sequence evolutionary models give almost model independent ages of 34-36Myr, with a precision of 10%. These ages are only slightly larger than the ages of 25-35(+/-5)Myr obtained using the same models to fit isochrones to higher mass stars descending towards the zero-age main-sequence, both in empirically calibrated and theoretical colour-magnitude diagrams. This agreement between age determinations in different mass ranges is an excellent test of the current generation of low-mass pre-main-sequence stellar models and lends confidence to ages determined with either method between 30 and 120Myr.
