- ID:
- ivo://CDS.VizieR/J/ApJ/822/97
- Title:
- Rotation-Activity Correlations in K-M dwarfs. I.
- Short Name:
- J/ApJ/822/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The reliable determination of rotation-activity correlations (RACs) depends on precise measurements of the following stellar parameters: T_eff_, parallax, radius, metallicity, and rotational speed vsini. In this paper, our goal is to focus on the determination of these parameters for a sample of K and M dwarfs. In a future paper (PaperII; Houdebine+, 2017, J/ApJ/837/96), we will combine our rotational data with activity data in order to construct RACs. Here, we report on a determination of effective temperatures based on the (R-I)_C_ color from the calibrations of Mann+ (2015, J/ApJ/804/64) and Kenyon & Hartmann (1995, J/ApJS/101/117) for four samples of late-K, dM2, dM3, and dM4 stars. We also determine stellar parameters (T_eff_, log(g), and [M/H]) using the principal component analysis-based inversion technique for a sample of 105 late-K dwarfs. We compile all effective temperatures from the literature for this sample. We determine empirical radius-[M/H] correlations in our stellar samples. This allows us to propose new effective temperatures, stellar radii, and metallicities for a large sample of 612 late-K and M dwarfs. Our mean radii agree well with those of Boyajian+ (2012, J/ApJ/757/112). We analyze HARPS and SOPHIE spectra of 105 late-K dwarfs, and we have detected vsini in 92 stars. In combination with our previous vsini measurements in M and K dwarfs, we now derive P/sini measures for a sample of 418 K and M dwarfs. We investigate the distributions of P/sini, and we show that they are different from one spectral subtype to another at a 99.9% confidence level.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/704/750
- Title:
- Rotational behavior of metal-poor stars
- Short Name:
- J/ApJ/704/750
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper describes the behavior of the rotational velocity in metal-poor stars ([Fe/H]<=-0.5dex) in different evolutionary stages, based on vsini values from the literature. Our sample is comprised of stars in the field and some Galactic globular clusters, including stars on the main sequence, the red giant branch (RGB), and the horizontal branch (HB). The metal-poor stars are, mainly, slow rotators, and their vsini distribution along the HR diagram is quite homogeneous. Nevertheless, a few moderate to high values of vsini are found in stars located on the main sequence and the HB. We show that the overall distribution of vsini values is basically independent of metallicity for the stars in our sample. We present an extensive tabulation of all quantities discussed in this paper, including rotation velocities, temperatures, gravities, and metallicities [Fe/H], as well as broadband magnitudes and colors.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/109
- Title:
- Rotational velocities + Li abundance in K giants
- Short Name:
- J/ApJ/757/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The orbital angular momentum of a close-orbiting giant planet can be sufficiently large that, if transferred to the envelope of the host star during the red giant branch (RGB) evolution, it can spin-up the star's rotation to unusually large speeds. This spin-up mechanism is one possible explanation for the rapid rotators detected among the population of generally slow-rotating red giant stars. These rapid rotators thus comprise a unique stellar sample suitable for searching for signatures of planet accretion in the form of unusual stellar abundances due to the dissemination of the accreted planet in the stellar envelope. In this study, we look for signatures of replenishment in the Li abundances and (to a lesser extent) ^12^C/^13^C, which are both normally lowered during RGB evolution. Accurate abundances were measured from high signal-to-noise echelle spectra for samples of both slow and rapid rotator red giant stars. We find that the rapid rotators are on average enriched in lithium compared to the slow rotators, but both groups of stars have identical distributions of ^12^C/^13^C within our measurement precision. Both of these abundance results are consistent with the accretion of planets of only a few Jupiter masses. We also explore alternative scenarios for understanding the most Li-rich stars in our sample--particularly Li regeneration during various stages of stellar evolution. Finally, we find that our stellar samples show non-standard abundances even at early RGB stages, suggesting that initial protostellar Li abundances and ^12^C/^13^C may be more variable than originally thought.
- ID:
- ivo://CDS.VizieR/J/ApJ/807/82
- Title:
- Rotational velocities of APOKASC red giants
- Short Name:
- J/ApJ/807/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the occurrence rate of rapidly rotating (vsini>10km/s), low-mass giant stars in the Apache Point Observatory Galaxy Evolution Experiment-Kepler (APOKASC) fields with asteroseismic mass and surface gravity measurements. Such stars are likely merger products and their frequency places interesting constraints on stellar population models. We also identify anomalous rotators, i.e., stars with 5km/s<vsini<10km/s that are rotating significantly faster than both angular momentum evolution predictions and the measured rates of similar stars. Our data set contains fewer rapid rotators than one would expect given measurements of the Galactic field star population, which likely indicates that asteroseismic detections are less common in rapidly rotating red giants. The number of low-mass moderate (5-10km/s) rotators in our sample gives a lower limit of 7% for the rate at which low-mass stars interact on the upper red giant branch because single stars in this mass range are expected to rotate slowly. Finally, we classify the likely origin of the rapid or anomalous rotation where possible. KIC 10293335 is identified as a merger product and KIC 6501237 is a possible binary system of two oscillating red giants.
- ID:
- ivo://CDS.VizieR/J/A+A/398/647
- Title:
- Rotational velocities of F and G stars
- Short Name:
- J/A+A/398/647
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed study of rotation and differential rotation analyzing high resolution high S/N spectra of 142 F-, G- and early K-type field stars. Using Least Squares Deconvolution we obtain broadening profiles for our sample stars and use the Fourier transform method to determine projected rotational velocities vsini. Distributions of rotational velocities and periods are studied in the HR-diagram. For a subsample of 32 stars of spectral type F0-G0 we derive the amount of differential rotation. We find evidence for differential rotation in ten of the 32 stars. The observations were done with the ESO 3.6m telescope at La Silla, Chile, in October 2000, October 2001 and April 2002. The CES instrument (resolution 235000) was used, in the wavelength regions 577-581nm and 322.5-627nm.
- ID:
- ivo://CDS.VizieR/J/A+A/634/L9
- Title:
- Rotation periods of 97 solar-like stars
- Short Name:
- J/A+A/634/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The accurate determination of stellar rotation periods is important for estimating stellar ages and for understanding stellar activity and evolution. While rotation periods can be determined for about thirty thousand stars in the Kepler field, there are over one hundred thousand stars, especially with low photometric variability and irregular pattern of variations, for which rotational periods are unknown. Here we investigate the effect of metallicity on the detectability of rotation periods. This is done by synthesising light curves of hypothetical stars that are identical to our Sun with the exception of the metallicity. These light curves are then used as an input to the period determination algorithms. We find that the success rate for recovering the rotation signal has a minimum close to the solar metallicity value. This can be explained by the compensation effect of facular and spot contributions. In addition, selecting solar-like stars with near-solar effective temperature and photometric variability, and with metallicity between M/H=-0.35 and M/H=0.35 from the Kepler sample, we analyse the fraction of stars for which rotational periods have been detected as a function of metallicity. In agreement with our theoretical estimate we find a local minimum for the detection fraction close to the solar metallicity. We further report rotation periods of 87 solar-like Kepler stars for the first time.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/92
- Title:
- RPA Southern Pilot Search of 107 Stars
- Short Name:
- J/ApJ/858/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recent detection of a binary neutron star merger and the clear evidence for the decay of radioactive material observed in this event have, after 60 years of effort, provided an astrophysical site for the rapid neutron- capture (r-) process which is responsible for the production of the heaviest elements in our universe. However, observations of metal-poor stars with highly-enhanced r-process elements have revealed abundance patterns suggesting that multiple sites may be involved. To address this issue and to advance our understanding of the r-process, we have initiated an extensive search for bright (V<13.5), very metal-poor ([Fe/H]<-2) stars in the Milky Way halo exhibiting strongly-enhanced r-process signatures. This paper presents the first sample collected in the southern hemisphere using the echelle spectrograph on du Pont 2.5m telescope at Las Campanas Observatory. We have observed and analyzed 107 stars with -3.13<[Fe/H]<-0.79. Of those, 12 stars are strongly enhanced in heavy r-process elements (r-II), 42 stars show moderate enhancements of heavy r-process material (r-I), and 20 stars exhibit low abundances of the heavy r-process elements and higher abundances of the light r-process elements relative to the heavy ones (limited-r). This search is more successful at finding r- process-enhanced stars compared to previous searches, primarily due to a refined target-selection procedure.
- ID:
- ivo://CDS.VizieR/J/ApJS/249/30
- Title:
- R-Process Alliance: metal-poor star spectroscopy
- Short Name:
- J/ApJS/249/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This compilation is the fourth data release from the R-Process Alliance (RPA) search for r-process-enhanced stars and the second release based on "snapshot" high-resolution (R~30000) spectra collected with the du Pont 2.5m Telescope. In this data release, we propose a new delineation between the r-I and r-II stellar classes at [Eu/Fe]=+0.7, instead of the empirically chosen [Eu/Fe]=+1.0 level previously in use, based on statistical tests of the complete set of RPA data released to date. We also statistically justify the minimum level of [Eu/Fe] for definition of the r-I stars, [Eu/Fe]>+0.3. Redefining the separation between r-I and r-II stars will aid in the analysis of the possible progenitors of these two classes of stars and determine whether these signatures arise from separate astrophysical sources at all. Applying this redefinition to previous RPA data, the number of identified r-II and r-I stars changes to 51 and 121, respectively, from the initial set of data releases published thus far. In this data release, we identify 21 new r-II, 111 new r-I (plus 3 re-identified), and 7 new (plus 1 re-identified) limited-r stars out of a total of 232 target stars, resulting in a total sample of 72 new r-II stars, 232 new r-I stars, and 42 new limited-r stars identified by the RPA to date.
- ID:
- ivo://CDS.VizieR/J/ApJ/868/110
- Title:
- R-Process Alliance: 1st release in Galactic halo
- Short Name:
- J/ApJ/868/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the detailed abundances and r-process classifications of 125 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were identified as metal-poor candidates from the RAdial Velocity Experiment (RAVE) and were followed up at high spectral resolution (R~31500) with the 3.5m telescope at Apache Point Observatory. The atmospheric parameters were determined spectroscopically from FeI lines, taking into account <3D> non-LTE corrections and using differential abundances with respect to a set of standards. Of the 125 new stars, 124 have [Fe/H]{<}-1.5, 105 have [Fe/H]{<}-2.0, and 4 have [Fe/H]{<}-3.0. Nine new carbon-enhanced metal-poor stars have been discovered, three of which are enhanced in r-process elements. Abundances of neutron-capture elements reveal 60 new r-I stars (with +0.3<=[Eu/Fe]<=+1.0 and [Ba/Eu]<0) and 4 new r-II stars (with [Eu/Fe]>+1.0). Nineteen stars are found to exhibit a "limited-r" signature ([Sr/Ba]>+0.5, [Ba/Eu]<0). For the r-II stars, the second- and third-peak main r-process patterns are consistent with the r-process signature in other metal-poor stars and the Sun. The abundances of the light, {alpha}, and Fe-peak elements match those of typical Milky Way (MW) halo stars, except for one r-I star that has high Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper motions from the second Gaia data release yield UVW space velocities for these stars that are consistent with membership in the MW halo. Intriguingly, all r-II and the majority of r-I stars have retrograde orbits, which may indicate an accretion origin.
- ID:
- ivo://CDS.VizieR/J/AJ/152/170
- Title:
- RRLs in globulars. IV. UBVRI photometry in Omega Cen
- Short Name:
- J/AJ/152/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New accurate and homogeneous optical UBVRI photometry has been obtained for variable stars in the Galactic globular cluster {omega} Cen (NGC 5139). We secured 8202 CCD images covering a time interval of 24 years and a sky area of 84x48arcmin. The current data were complemented with data available in the literature and provided new, homogeneous pulsation parameters (mean magnitudes, luminosity amplitudes, periods) for 187 candidate {omega} Cen RR Lyrae (RRLs). Among them we have 101 RRc (first overtone) and 85 RRab (fundamental) variables, and a single candidate RRd (double-mode) variable. Candidate Blazhko RRLs show periods and colors that are intermediate between the RRc and RRab variables, suggesting that they are transitional objects. A comparison of the period distribution and the Bailey diagram indicates that RRLs in {omega} Cen show a long-period tail not present in typical Oosterhoff II (OoII) globulars. The RRLs in dwarf spheroidals and in ultra-faint dwarfs have properties between Oosterhoff intermediate and OoII clusters. Metallicity plays a key role in shaping the above evidence. These findings do not support the hypothesis that {omega} Cen is the core remnant of a spoiled dwarf galaxy. Using optical period-Wesenheit relations that are reddening-free and minimally dependent on metallicity we find a mean distance to {omega} Cen of 13.71+/-0.08+/-0.01mag (semi-empirical and theoretical calibrations). Finally, we invert the I-band period-luminosity-metallicity relation to estimate individual RRLs' metal abundances. The metallicity distribution agrees quite well with spectroscopic and photometric metallicity estimates available in the literature.
