- ID:
- ivo://CDS.VizieR/J/ApJ/837/96
- Title:
- Rotation-Activity Correlations in K-M dwarfs II.
- Short Name:
- J/ApJ/837/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the rotation-activity correlations (RACs) in a sample of stars from spectral type dK4 to dM4. We study RACs using chromospheric data and coronal data. We study the Ca II line surface fluxes-P/sini RACs. We fit the RACs with linear homoscedastic and heteroscedastic regression models. We find that these RACs differ substantially from one spectral sub-type to another. For dM3 and dM4 stars, we find that the RACs cannot be described by a simple model, but instead that there may exist two distinct RAC behaviors for the low-activity and the high-activity stellar sub-samples, respectively. Although these results are preliminary and will need confirmation, the data suggest that these distinct RACs may be associated with different dynamo regimes. We also study R'_HK_ as a function of the Rossby number R_0_. We find (i) for dK4 stars, R'_HK_ as a function of R_0_ agrees well with previous results for F-G-K stars and (ii) in dK6, dM2, dM3, and dM4 stars, at a given R_0_, the values of R'_HK_ lie at a factor of 3, 10, 20, and 90, respectively, below the F-G-K RAC. Our results suggest a significant decrease in the efficiency of the dynamo mechanism(s) as regards chromospheric heating before and at dM3, i.e., before and at the transition to complete convection. We also show that the ratio of coronal heating to chromospheric heating L_X_/L_HK_ increases by a factor of 100 between dK4 and dM4 stars.
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- ID:
- ivo://CDS.VizieR/J/AJ/156/275
- Title:
- Rotational evolution of young, binary M dwarfs
- Short Name:
- J/AJ/156/275
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed K2 light curves for more than 3000 low-mass stars in the ~8 Myr old Upper Sco association, the ~125 Myr age Pleiades open cluster, and the ~700 Myr old Hyades and Praesepe open clusters to determine stellar rotation rates. Many of these K2 targets show two distinct periods, and for the lowest-mass stars in these clusters, virtually all of these systems with two periods are photometric binaries. The most likely explanation is that we are detecting the rotation periods for both components of these binaries. We explore the evolution of the rotation rate in both components of photometric binaries relative to one another and to nonphotometric binary stars. In Upper Sco and the Pleiades, these low-mass binary stars have periods that are much shorter on average and much closer to each other than would be true if drawn at random from the M dwarf single stars. In Upper Sco, this difference correlates strongly with the presence or absence of infrared excesses due to primordial circumstellar disks-the single-star population includes many stars with disks, and their rotation periods are distinctively longer on average than their binary star cousins of the same mass. By Praesepe age, the significance of the difference in rotation rate between the single and binary low-mass M dwarf stars is much less, suggesting that angular momentum loss from winds for fully convective zero-age main-sequence stars erases memory of the rotation rate dichotomy for binary and single very low mass stars at later ages.
- ID:
- ivo://CDS.VizieR/J/ApJ/704/975
- Title:
- Rotational velocities for M dwarfs
- Short Name:
- J/ApJ/704/975
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectroscopic rotation velocities (vsini) for 56 M dwarf stars using high-resolution Hobby-Eberly Telescope High Resolution Spectrograph red spectroscopy. In addition, we have also determined photometric effective temperatures, masses, and metallicities ([Fe/H]) for some stars observed here and in the literature where we could acquire accurate parallax measurements and relevant photometry. We have increased the number of known vsini values for mid M stars by around 80% and can confirm a weakly increasing rotation velocity with decreasing effective temperature. Our sample of vsini is peak at low velocities (~3km/s). We find a change in the rotational velocity distribution between early M and late M stars, which is likely due to the changing field topology between partially and fully convective stars. There is also a possible further change in the rotational distribution toward the late M dwarfs where dust begins to play a role in the stellar atmospheres. We also link vsini to age and show how it can be used to provide mid-M star age limits. When all literature velocities for M dwarfs are added to our sample, there are 198 with vsini<=10km/s and 124 in the mid-to-late M star regime (M3.0-M9.5) where measuring precision optical radial velocities is difficult. In addition, we also search the spectra for any significant Half emission or absorption. Forty three percent were found to exhibit such emission and could represent young, active objects with high levels of radial-velocity noise. We acquired two epochs of spectra for the star GJ1253 spread by almost one month and the Half profile changed from showing no clear signs of emission, to exhibiting a clear emission peak. Four stars in our sample appear to be low-mass binaries (GJ1080, GJ3129, Gl802, and LHS3080), with both GJ3129 and Gl802 exhibiting double Half emission features. The tables presented here will aid any future M star planet search target selection to extract stars with low vsini.
- ID:
- ivo://CDS.VizieR/J/AJ/143/93
- Title:
- Rotational velocities in early-M stars
- Short Name:
- J/AJ/143/93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of rotation and chromospheric activity in a sample of 334 M dwarfs of spectral types M0-M4.5 populating the parameter space around the boundary to full convection. We obtain high-resolution optical spectra for 206 targets and determine projected rotational velocity, vsin i, and H{alpha} emission. The data are combined with measurements of vsin i in field stars of the same spectral type from the literature. Our sample adds 157 new rotation measurements to the existing literature and almost doubles the sample of available vsin i. The final sample provides a statistically meaningful picture of rotation and activity at the transition to full convection in the solar neighborhood. Finally, we compare projected rotational velocities of 33 stars to rotational periods derived from photometry in the literature and determine inclinations for a few of them.
- ID:
- ivo://CDS.VizieR/J/A+A/331/581
- Title:
- Rotation and activity in field M dwarfs
- Short Name:
- J/A+A/331/581
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained high resolution spectra for a volume-limited sample of 118 field M dwarfs. From these observations we derive projected rotational velocities and fluxes in the H{alpha} and H{beta} lines. 8 stars are double-lined spectroscopic binaries with measured or probable periods short enough for rotation to be tidally synchronized with the orbit, and another 11 are visual binaries where we cannot yet separate the lines of the two stars. Of the remaining 99 stars, 24 have rotational velocities above our detection limit of ~2km/s, and some are quite fast rotators, including two with vsini>30km/s and one with vsini~50km/s. Given the small radii of M dwarfs, these moderate rotational velocities correspond to rather short maximum rotational periods, of only 7-8 hours.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/93
- Title:
- Rotation & Galactic kinematics of mid M dwarfs
- Short Name:
- J/ApJ/821/93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotation is a directly observable stellar property, and it drives magnetic field generation and activity through a magnetic dynamo. Main-sequence stars with masses below approximately 0.35M_{sun}_ (mid-to-late M dwarfs) are fully convective, and are expected to have a different type of dynamo mechanism than solar-type stars. Measurements of their rotation rates provide insight into these mechanisms, but few rotation periods are available for these stars at field ages. Using photometry from the MEarth Project, we measure rotation periods for 387 nearby, mid-to-late M dwarfs in the northern hemisphere, finding periods from 0.1 to 140 days. The typical rotator has stable, sinusoidal photometric modulations at a semi-amplitude of 0.5%-1%. We find no period-amplitude relation for stars below 0.25M_{sun}_ and an anticorrelation between period and amplitude for higher-mass M dwarfs. We highlight the existence of older, slowly rotating stars without H{alpha} emission that nevertheless have strong photometric variability. We use parallaxes, proper motions, radial velocities, photometry, and near-infrared metallicity estimates to further characterize the population of rotators. The Galactic kinematics of our sample is consistent with the local population of G and K dwarfs, and rotators have metallicities characteristic of the solar neighborhood. We use the W space velocities and established age-velocity relations to estimate that stars with P<10d have ages of on average <2Gyr, and that those with P>70d have ages of about 5Gyr. The period distribution is dependent on mass: as the mass decreases, the slowest rotators at a given mass have longer periods, and the fastest rotators have shorter periods. We find a lack of stars with intermediate rotation periods, and the gap between the fast and slow rotators is larger for lower masses. Our data are consistent with a scenario in which these stars maintain rapid rotation for several gigayears, then spin down quickly, reaching periods of around 100d by a typical age of 5Gyr.
- ID:
- ivo://CDS.VizieR/J/MNRAS/432/1203
- Title:
- Rotation periods of M-dwarf stars
- Short Name:
- J/MNRAS/432/1203
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analysed 10 months of public data from the Kepler space mission to measure rotation periods of main-sequence stars with masses between 0.3 and 0.55M_{sun}_. To derive the rotational period, we introduce the autocorrelation function and show that it is robust against phase and amplitude modulation and residual instrumental systematics. Of the 2483 stars examined, we detected rotation periods in 1570 (63.2%), representing an increase of a factor of ~30 in the number of rotation period determination for field M dwarfs. The periods range from 0.37 to 69.7d, with amplitudes ranging from 1.0 to 140.8mmag. The rotation period distribution is clearly bimodal, with peaks at ~19 and ~33d, hinting at two distinct waves of star formation, a hypothesis that is supported by the fact that slower rotators tend to have larger proper motions. The two peaks of the rotation period distribution form two distinct sequences in period-temperature space, with the period decreasing with increasing temperature, reminiscent of the Vaughan-Preston gap. The period-mass distribution of our sample shows no evidence of a transition at the fully convective boundary. On the other hand, the slope of the upper envelope of the period-mass relation changes sign around 0.55M_{sun}_, below which period rises with decreasing mass.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A135
- Title:
- RS Cnc IRAM NOEMA interferometric data
- Short Name:
- J/A+A/658/A135
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The latest evolutionary phases of low- and intermediate mass stars are characterized by complex physical processes like turbulence, convection, stellar pulsations, magnetic fields, condensation of solid particles, and the formation of massive outflows that inject freshly produced heavy elements and dust particles into the interstellar medium. By investigating individual objects in detail we wish to analyze and disentangle the effects of the interrelated physical processes on the structure of the wind forming region around these objects. We use the Northern Extended Millimeter Array (NOEMA) to obtain spatially and spectrally resolved observations of the semi-regular Asymptotic Giant Branch star RS Cancri to shed light on the morpho-kinematic structure of its inner, wind forming environment by applying detailed 3-D reconstruction modeling and LTE radiative transfer calculations. We detect 32 lines of 13 molecules and isotopologs (CO, SiO, SO, SO_2_, H_2_O, HCN, PN), including several transitions from vibrationally excited states. HCN, H^13^CN, millimeter vibrationally excited H_2_O, SO, ^34^SO, SO_2_, and PN are detected for the first time in RS Cnc. Evidence for rotation is seen in HCN, SO, SO_2_, and SiO(v=1). From CO and SiO channel maps, we find an inner, equatorial density enhancement, and a bipolar outflow structure with a mass loss rate of 1x10^-7^M_{sun}_/yr for the equatorial region and of 2x10^-7^M_{sun}_/yr for the polar outflows. The ^12^CO/^13^CO ratio is measured to be ~20 on average, 24+/-2 in the polar outflows and 19+/-3 in the equatorial region. We do not find direct evidence of a companion that might explain this kind of kinematic structure, and explore the possibility that a magnetic field might be the cause of it. The innermost molecular gas is influenced by stellar pulsation and possibly by convective cells that leave their imprint on broad wings of certain molecular lines, such as SiO and SO. RS Cnc is one of the few nearby, low mass-loss-rate, oxygen-rich AGB stars with a wind displaying both an equatorial disk and bipolar outflows. Its orientation with respect to the line of sight is particularly favorable for a reliable study of its morpho-kinematics. The mechanism causing early spherical symmetry breaking remains however uncertain, calling for additional high spatial and spectral resolution observations of the emission of different molecules in different transitions, along with a deeper investigation of the coupling among the different physical processes at play.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/26
- Title:
- Runaway M dwarf candidates from SDSS-DR7
- Short Name:
- J/ApJ/813/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 20 runaway M dwarf candidates (RdMs) within 1kpc of the Sun whose Galactocentric (GC) velocities exceed 400km/s. The candidates were selected from the Sloan Digital Sky Survey (SDSS) DR7 M Dwarf Catalog of West et al. (2011, J/AJ/141/97). Our RdMs have SDSS+USNO-B proper motions that are consistent with those recorded in the PPMXL, LSPM, and combined Wide-field Infrared Survey Explorer+SDSS+Two-micron All-sky Survey catalogs. Sixteen RdMs are classified as dwarfs, while the remaining four RdMs are subdwarfs. We model the Galactic potential using a bulge-disk-halo profile. Our fastest RdM, with a GC velocity of 658.5+/-236.9km/s, is a possible hypervelocity candidate, as it is unbound in 77% of our simulations. About half of our RdMs have kinematics that are consistent with ejection from the Galactic center. Seven of our RdMs have kinematics consistent with an ejection scenario from M31 or M32 to within 2{sigma}, although our distance-limited survey makes such a realization unlikely. No more than four of our RdMs may have originated from the Leo stream. We propose that to within measurement errors, most of our bound RdMs are likely disk runaways or halo objects, and may have been accelerated through a series of multi-body interactions within the Galactic disk or possibly supernovae explosions.
- ID:
- ivo://CDS.VizieR/J/AJ/159/290
- Title:
- RVs of 12 spectroscopic binaries M-dwarfs
- Short Name:
- J/AJ/159/290
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the spectroscopic orbits of 11 nearby, mid-to-late M dwarf binary systems in a variety of configurations: 2 single-lined binaries (SB1s), 7 double-lined binaries (SB2s), 1 double-lined triple (ST2), and 1 triple-lined triple (ST3). Eight of these orbits are the first published for these systems, while five are newly identified multiples. We obtained multi-epoch, high-resolution spectra with the TRES instrument on the 1.5m Tillinghast Reflector at the Fred Lawrence Whipple Observatory located on Mt. Hopkins in AZ. Using the TiO molecular bands at 7065-7165{AA}, we calculated radial velocities for these systems, from which we derived their orbits. We find LHS 1817 to have in a 7hr period a companion that is likely a white dwarf, due to the ellipsoidal modulation we see in our MEarth-North light-curve data. We find G123-45 and LTT11586 to host companions with minimum masses of 41MJup and 44MJup with orbital periods of 35 and 15days, respectively. We find 2MA0930+0227 to have a rapidly rotating stellar companion in a 917 day orbital period. GJ268, GJ1029, LP734-34, GJ1182, G258-17, and LTT7077are SB2s with stellar companions with orbital periods of 10, 96, 34, 154, 5, and 84days; LP655-43 is an ST3 with one companion in an 18day orbital period and an outer component in a longer undetermined period. In addition, we present radial velocities for both components of L870-44AB and for the outer components of LTT11586 and LP655-43.
