Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA Photometric Variability Survey of Field K and M Dwarf Stars with HATNet
157
0
0.0
(
0
)
Authors
J.D. Hartman
Ask ChatGPT about the research
No Arabic abstract
Using light curves from the HATNet survey for transiting extrasolar planets we investigate the optical broad-band photometric variability of a sample of 27,560 field K and M dwarfs selected by color and proper-motion. A total of 2120 stars exhibit potential variability, including 95 stars with eclipses and 60 stars with flares. Based on a visual inspection of these light curves and an automated blending classification, we select 1568 stars, including 78 eclipsing binaries, as secure variable star detections that are not obvious blends. We estimate that a further ~26% of these stars may be blends with fainter variables, though most of these blends are likely to be among the hotter stars in our sample. We find that only 38 of the 1568 stars, including 5 of the eclipsing binaries, have previously been identified as variables or are blended with previously identified variables. One of the newly identified eclipsing binaries is 1RXS J154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, for which we derive preliminary estimates for the component masses and radii of M_1 = M_2 = 0.258 +- 0.008 M_Sun and R_1 = R_2 = 0.289 +- 0.007 R_Sun. The radii of the component stars are larger than theoretical expectations if the system is older than ~200 Myr. The majority of the variables are heavily spotted BY Dra-type stars for which we determine rotation periods. Using this sample, we investigate the relations between period, color, age, and activity measures, including optical flaring, for K and M dwarfs., finding that many of the well-established relations for F, G and K dwarfs continue into the M dwarf regime (Abridged).
rate research
Read More
This work brings a wavelet analysis for 14 Kepler white dwarf stars, in order to confirm their photometric variability behavior and to search for periodicities in these targets. From the observed Kepler light curves we obtained the wavelet local and global power spectra. Through this procedure, one can perform an analysis in time-frequency domain rich in details, and so to obtain a new perspective on the time evolution of the periodicities present in these stars. We identified a photometric variability behavior in ten white dwarfs, corresponding to period variations of ~ 2 h to 18 days: among these stars, three are new candidates and seven, earlier identified from other studies, are confirmed.
We present here optical I-band photometric variability study down to $simeq$ 19 mag of a young ($sim$2-3 Myr) star-forming region IC 348 in the Perseus molecular cloud. We aim to explore the fast rotation (in the time-scales of hours) in Very Low Mass stars (VLMs) including Brown Dwarfs (BDs). From a sample of 177 light-curves using our new I-band observations, we detect new photometric variability in 22 young M-dwarfs including 6 BDs, which are bonafide members in IC 348 and well-characterized in the spectral type of M-dwarfs. Out of 22 variables, 11 M dwarfs including one BD show hour-scale periodic variability in the period range 3.5 - 11 hours and rest are aperiodic in nature. Interestingly, an optical flare is detected in a young M2.75 dwarf in one night data on 20 December 2016. From the flare light curve, we estimate the emitted flared energy of 1.48 $times$ 10$^{35}$ ergs. The observed flared energy with an uncertainty of tens of per cent is close to the super-flare range ($sim$ 10$^{34}$ ergs), which is rarely observed in active M dwarfs.
We present a survey of far-ultraviolet (FUV; 1150 - 1450 Ang) emission line spectra from 71 planet-hosting and 33 non-planet-hosting F, G, K, and M dwarfs with the goals of characterizing their range of FUV activity levels, calibrating the FUV activity level to the 90 - 360 Ang extreme-ultraviolet (EUV) stellar flux, and investigating the potential for FUV emission lines to probe star-planet interactions (SPIs). We build this emission line sample from a combination of new and archival observations with the Hubble Space Telescope-COS and -STIS instruments, targeting the chromospheric and transition region emission lines of Si III, N V, C II, and Si IV. We find that the exoplanet host stars, on average, display factors of 5 - 10 lower UV activity levels compared with the non-planet hosting sample; this is explained by a combination of observational and astrophysical biases in the selection of stars for radial-velocity planet searches. We demonstrate that UV activity-rotation relation in the full F - M star sample is characterized by a power-law decline (with index $alpha$ ~ -1.1), starting at rotation periods >~3.5 days. Using N V or Si IV spectra and a knowledge of the stars bolometric flux, we present a new analytic relationship to estimate the intrinsic stellar EUV irradiance in the 90 - 360 Ang band with an accuracy of roughly a factor of ~2. Finally, we study the correlation between SPI strength and UV activity in the context of a principal component analysis that controls for the sample biases. We find that SPIs are not a statistically significant contributor to the observed UV activity levels.
Brightness variations due to dark spots on the stellar surface encode information about stellar surface rotation and magnetic activity. In this work, we analyze the Kepler long-cadence data of 26,521 main-sequence stars of spectral types M and K in order to measure their surface rotation and photometric activity level. Rotation-period estimates are obtained by the combination of a wavelet analysis and autocorrelation function of the light curves. Reliable rotation estimates are determined by comparing the results from the different rotation diagnostics and four data sets. We also measure the photometric activity proxy Sph using the amplitude of the flux variations on an appropriate timescale. We report rotation periods and photometric activity proxies for about 60 per cent of the sample, including 4,431 targets for which McQuillan et al. (2013a,2014) did not report a rotation period. For the common targets with rotation estimates in this study and in McQuillan et al. (2013a,2014), our rotation periods agree within 99 per cent. In this work, we also identify potential polluters, such as misclassified red giants and classical pulsator candidates. Within the parameter range we study, there is a mild tendency for hotter stars to have shorter rotation periods. The photometric activity proxy spans a wider range of values with increasing effective temperature. The rotation period and photometric activity proxy are also related, with Sph being larger for fast rotators. Similar to McQuillan et al. (2013a,2014), we find a bimodal distribution of rotation periods.
We report the discovery by the HATNet survey of HAT-TR-318-007, a $P = 3.34395390pm0.00000020$ d period detached double-lined M-dwarf binary with total secondary eclipses. We combine radial velocity (RV) measurements from TRES/FLWO 1.5 m, and time-series photometry from HATNet, FLWO 1.2 m, BOS 0.8 m and NASA K2 Campaign 5, to determine the masses and radii of the component stars: $M_{A} = 0.448pm0.011$ $M_{odot}$, $M_{B} = 0.2721^{+0.0041}_{-0.0042}$ $M_{odot}$, $R_{A} = 0.4548^{+0.0035}_{-0.0036}$ $R_{odot}$, and $R_{B} = 0.2913^{+0.0023}_{-0.0024}$ $R_{odot}$. We obtained a FIRE/Magellan near-infrared spectrum of the primary star during a total secondary eclipse, and use this to obtain disentangled spectra of both components. We determine spectral types of ST$_{A} = {rm M}3.71pm0.69$ and ST$_{B} = {rm M}5.01pm0.73$, and effective temperatures of T$_{rm eff,A} = 3190pm110$ K and T$_{rm eff,B} = 3100pm110$ K, for the primary and secondary star, respectively. We also measure a metallicity of [Fe/H]$=+0.298pm0.080$ for the system. We find that the system has a small, but significant, non-zero eccentricity of $0.0136pm0.0026$. The K2 light curve shows a coherent variation at a period of $3.41315^{+0.00030}_{-0.00032}$ d, which is slightly longer than the orbital period, and which we demonstrate comes from the primary star. We interpret this as the rotation period of the primary. We perform a quantitative comparison between the Dartmouth stellar evolution models and the seven systems, including HAT-TR-318-007, that contain M dwarfs with $0.2 M_{odot} < M < 0.5 M_{odot}$, have metallicity measurements, and have masses and radii determined to better than 5% precision. Discrepancies between the predicted and observed masses and radii are found for three of the systems.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
