- ID:
- ivo://CDS.VizieR/J/ApJ/814/35
- Title:
- Flare events in M dwarf of M37
- Short Name:
- J/ApJ/814/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on one-month long MMT time-series observations of the open cluster M37, we monitored light variations of nearly 2500 red dwarfs and successfully identified 420 flare events from 312 cluster M dwarf stars. For each flare light curve, we derived observational and physical parameters, such as flare shape, peak amplitude, duration, energy, and peak luminosity. We show that cool stars produce serendipitous flares energetic enough to be observed in the r-band, and their temporal and peak characteristics are almost the same as those in traditional U-band observations. We also found many large-amplitude flares with inferred {Delta}u>6mag in the cluster sample which had been rarely reported in previous ground-based observations. Following the ergodic hypothesis, we investigate in detail statistical properties of flare parameters over a range of energy (E_r_~=10^31^-10^34^erg). As expected, there are no statistical differences in the distributions of flare timescales, energies, and frequencies among stars of the same age and mass group. We note that our sample tend to have longer rise and decay timescales compared to those seen in field flare stars of the same spectral type and be more energetic. Flare frequency distributions follow power-law distributions with slopes {beta}~0.62-1.21 for all flare stars and {beta}~0.52-0.97 for stars with membership information (P_mem_>=0.2). These are in general agreement with previous works on flare statistics of young open clusters and nearby field stars. Our results give further support to the classical age-activity relations.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/645/A42
- Title:
- Flares in 5 open clusters
- Short Name:
- J/A+A/645/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetic fields are a key component in the main sequence evolution of low mass stars. Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. The occurrence rates and energy distributions of flares trace stellar characteristics such as mass and age. But before flares can be used to constrain stellar properties, the flaring-age-mass relation requires proper calibration. This work sets out to quantify flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite. Drawing from the complete K2 archive, we searched 3435 80 day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6Gyr (M67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690Myr) to the sample as a comparison cluster to Praesepe (750Myr), the 2.6Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. We found that the flare energy distribution was similar in the entire parameter space, following a power law relation with an exponent between 1.84 and 2.39. We confirmed that flaring rates declined with age, and declined faster for higher mass stars. Our results are in good agreement with most previous statistical flare studies. We found evidence that a rapid decline in flaring activity occurred in M1-M2 dwarfs around Hyades/Praesepe age, when these stars spun down to rotation periods of about 10 d, while higher mass stars had already transitioned to lower flaring rates, and lower mass stars still resided in the saturated activity regime. We conclude that some discrepancies between our results and flare studies that used rotation periods for their age estimates could be explained by sample selection bias toward more active stars, but others may hint at limitations of using rotation as an age indicator without additional constraints from stellar activity.
- ID:
- ivo://CDS.VizieR/J/AJ/140/483
- Title:
- Flares of UV Cet type stars
- Short Name:
- J/AJ/140/483
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this study, a new method is presented to classify flares derived from the photoelectric photometry of UV Ceti type stars. This method is based on statistical analyses using an independent samples t-test. The data used in analyses were obtained from four flare stars observed between 2004 and 2007. The total number of flares obtained in the observations of AD Leo, EV Lac, EQ Peg, and V1054 Oph is 321 in the standard Johnson U band. As a result flares can be separated into two types, slow and fast, depending on the ratio of flare decay time to flare rise time. The ratio is below 3.5 for all slow flares, while it is above 3.5 for all fast flares. Also, according to the independent samples t-test, there is a difference of about 157 s between equivalent durations of slow and fast flares. In addition, there are significant differences between amplitudes and rise times of slow and fast flares.
1974. "flip-flop" in FK Com
- ID:
- ivo://CDS.VizieR/J/A+A/282/L9
- Title:
- "flip-flop" in FK Com
- Short Name:
- J/A+A/282/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/723/1469
- Title:
- Flux calibrations and WZ Oph photometry
- Short Name:
- J/ApJ/723/1469
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Among several EB distance algorithms, direct comparison of observed and theoretical fluxes is particularly straightforward, although it requires absolute flux calibrations for which only a modest number of publications exist. Here, we measure UBV RI and uvby flux calibrations and calibration ratios from astronomical objects in ways not previously tried, specifically for EBs, single stars within 80pc, and the Sun. All of the single stars are below about 6500K temperature. Interstellar extinction is avoided by a restriction to nearby targets. Some photometric band calibrations in the literature are accurate enough for very good EB distance determinations if star temperatures are accurately known, especially considering that estimated distance has only a square-root dependence on calibration constant, but accurate band-to-band calibration ratios are keys to the combined temperature-distance problem. Band-independent canceling factors (star radii and distances) allow calibration ratio measurement with enhanced accuracy, compared to individual band calibrations. A physical EB model with embedded stellar atmosphere emission optimally matches theory to observations for the binaries. Single star candidates are identified as reliably single if their radial velocity variations are below 100m/s. For the most part, we find good agreement with some of the previous calibrations and the ratios are improved.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/553
- Title:
- Fluxes in nearby star-forming galaxies
- Short Name:
- J/ApJ/706/553
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Compared to starburst galaxies, normal star-forming galaxies have been shown to display a much larger dispersion of the dust attenuation at fixed reddening through studies of the IRX-{beta} diagram (the IR/UV ratio "IRX" versus the UV color "{beta}"). To investigate the causes of this larger dispersion and attempt to isolate second parameters, we have used GALEX UV, ground-based optical, and Spitzer infrared imaging of eight nearby galaxies, and examined the properties of individual UV and 24um selected star-forming regions. We concentrated on star-forming regions, in order to isolate simpler star formation histories than those that characterize whole galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/864/71
- Title:
- Fluxes & physical param. of blended YSOs
- Short Name:
- J/ApJ/864/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite significant evidence suggesting that intermediate- and high-mass stars form in clustered environments, how stars form when the available resources are shared is still not well understood. A related question is whether the initial mass function (IMF) is in fact universal across galactic environments, or whether it is an average of IMFs that differ, for example, in massive versus low-mass molecular clouds. One of the long-standing problems in resolving these questions and in the study of young clusters is observational: how to accurately combine multiwavelength data sets obtained using telescopes with different spatial resolutions. The resulting confusion hinders our ability to fully characterize clustered star formation. Here we present a new method that uses Bayesian inference to fit the blended spectral energy distributions and images of individual young stellar objects (YSOs) in confused clusters. We apply this method to the infrared photometry of a sample comprising 70 Spitzer-selected, low-mass (M_cl_<100M_{sun}_) young clusters in the galactic plane, and we use the derived physical parameters to investigate how the distribution of YSO masses within each cluster relates to the total mass of the cluster. We find that for low-mass clusters this distribution is indistinguishable from a randomly sampled Kroupa IMF for this range of cluster masses. Therefore, any effects of self-regulated star formation that affect the IMF sampling are likely to play a role only at larger cluster masses. Our results are also compatible with smoothed particle hydrodynamics models that predict a dynamical termination of the accretion in protostars, with massive stars undergoing this stopping at later times in their evolution.
- ID:
- ivo://CDS.VizieR/J/AJ/159/100
- Title:
- Flux & RVs of the dwarf G9-40 with K2 & HPF
- Short Name:
- J/AJ/159/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We validate the discovery of a 2-Earth-radii sub-Neptune-sized planet around the nearby high-proper-motion M2.5 dwarf G9-40 (EPIC212048748), using high-precision, near-infrared (NIR) radial velocity (RV) observations with the Habitable-zone Planet Finder (HPF), precision diffuser-assisted ground-based photometry with a custom narrowband photometric filter, and adaptive optics imaging. At a distance of d=27.9pc, G9-40b is the second-closest transiting planet discovered by K2 to date. The planet's large transit depth (~3500ppm), combined with the proximity and brightness of the host star at NIR wavelengths (J=10, K=9.2), makes G9-40b one of the most favorable sub-Neptune-sized planets orbiting an M dwarf for transmission spectroscopy with James Webb Space Telescope, ARIEL, and the upcoming Extremely Large Telescopes. The star is relatively inactive with a rotation period of ~29days determined from the K2 photometry. To estimate spectroscopic stellar parameters, we describe our implementation of an empirical spectral-matching algorithm using the high-resolution NIR HPF spectra. Using this algorithm, we obtain an effective temperature of Teff=3404{+/-}73K and metallicity of [Fe/H]=-0.08{+/-}0.13. Our RVs, when coupled with the orbital parameters derived from the transit photometry, exclude planet masses above 11.7M{Earth} with 99.7% confidence assuming a circular orbit. From its radius, we predict a mass of M=5.0_-1.9_^+3.8^M_{Earth}_ and an RV semiamplitude of K=4.1_-1.6_^+3.1^m/s, making its mass measurable with current RV facilities. We urge further RV follow-up observations to precisely measure its mass, to enable precise transmission spectroscopic measurements in the future.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/3
- Title:
- Follow-up LCs of 2 Spitzer microlensing events
- Short Name:
- J/ApJ/891/3
- Date:
- 17 Jan 2022 00:32:54
- Publisher:
- CDS
- Description:
- We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a 0.60+/-0.03M_{sun}_ star with DLS=0.53+/-0.11kpc, where DLS is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a 0.51_-0.10_^+0.12^M_{sun}_ star with DLS=0.40+/-0.12kpc or a 0.38_-0.12_^+0.13^M_{sun} star with DLS=0.53+/-0.19kpc. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite- source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurring in single-lens events.
- ID:
- ivo://CDS.VizieR/J/ApJ/724/866
- Title:
- Follow-up observations of HAT-P-15
- Short Name:
- J/ApJ/724/866
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of HAT-P-15b, a transiting extrasolar planet in the "period valley," a relatively sparsely populated period regime of the known extrasolar planets. The host star, GSC 2883-01687, is a G5 dwarf with V=12.16. It has a mass of 1.01+/-0.04M_{sun}_, radius of 1.08+/-0.04R_{sun}_, effective temperature 5568+/-90K, and metallicity [Fe/H]=+0.22+/-0.08. The planetary companion orbits the star with a period P=10.863502+/-0.000027 days, transit epoch T_c_=2454638.56019+/-0.00048(BJD), and transit duration 0.2285+/-0.0015days. It has a mass of 1.946+/-0.066M_J_ and radius of 1.072+/-0.043R_J_ yielding a mean density of 1.96+/-0.22g/cm^3^. At an age of 6.8^+2.5^_-1.6_Gyr, the planet is H/He-dominated and theoretical models require about 2% (10M_{earth}_) worth of heavy elements to reproduce its measured radius. With an estimated equilibrium temperature of ~820K during transit, and ~1000K at occultation, HAT-P-15b is a potential candidate to study moderately cool planetary atmospheres by transmission and occultation spectroscopy.
