- ID:
- ivo://CDS.VizieR/J/A+A/656/A103
- Title:
- NGC 3532 stars cChromospheric activity
- Short Name:
- J/A+A/656/A103
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The coeval stars of young open clusters provide insights into the formation of the rotation-activity relationship that elude studies of multi-age field populations. We measure the chromospheric activity of cool stars in the 300 Myr old open cluster NGC 3532 in concert with their rotation periods to study the mass-dependent morphology of activity for this transitional coeval population. Using multi-object spectra of the Ca II infrared triplet region obtained with the AAOmega spectrograph at the 4m Anglo- Australian Telescope, we measure the chromospheric emission ratios R'_IRT_ for 454 FGKM cluster members of NGC3532. The morphology of activity against colour appears to be a near-mirror image of the cluster's rotational behaviour. In particular, we identify a group of 'desaturated transitional rotators' that branches off from the main group of unsaturated FGK slow rotators, and from which it is separated by an 'activity gap'. The few desaturated gap stars are identical to the ones in the rotational gap. Nevertheless, the rotation-activity diagram is completely normal. In fact, the relationship is so tight that it allows us to predict rotation periods for many additional stars. We then precisely determine these periods from our photometric light curves, allowing us to construct an enhanced colour-period diagram that represents 66% of the members in our sample. Our activity measurements show that all fast rotators of near-solar mass (F-G type) have evolved to become slow rotators, demonstrating that the absence of fast rotators in a colour-period diagram is not a detection issue but an astrophysical fact. We also identify a new population of low-activity stars among the early Mdwarfs, enabling us to populate the extended slow rotator sequence in the colour-period diagram. The joint analysis of chromospheric activity and photometric time series data thus enables comprehensive insights into the evolution of the rotation and activity of stars during the transitional phase between the Pleiades and Hyades ages.
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Search Results
- ID:
- ivo://CDS.VizieR/J/PASP/121/827
- Title:
- NIR fluxes for 35 HR late-type stars
- Short Name:
- J/PASP/121/827
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New semicontinuous scans (with nearly contiguous passbands) are presented for alpha CMi and for 24 G and K giants. In addition, 12 such scans published in 1984 are reduced to an up-to-date standard-star system and adopted. The collected scans range from 3288{AA} to at least 6940{AA}, and they have been standardized to a system defined by alpha Lyr. They are supplemented by measurements of 23 of the program giants using six near-infrared passbands. Tests of the consistency and accuracy of the data yield encouraging results.
- ID:
- ivo://CDS.VizieR/J/A+A/503/639
- Title:
- NIR spectral of M-T dwarfs
- Short Name:
- J/A+A/503/639
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present complete near-infrared (0.85-2.45um), low-resolution (R~100) spectra of a sample of 54 disk M-, L-, and T-dwarfs with reliable optical or near infrared spectral-type classification from the literature. The observations were obtained with a prism-based optical element, the Amici device, which provides a complete spectrum of the source on the detector. Our observations indicate that low-resolution near-infrared spectroscopy can be used to determine the spectral classification of late-type field dwarfs in a fast but accurate way. We derive a set of near-infrared spectral indices that are useful to the classification of field dwarfs not seriously affected by reddening. Finally, we show that the comparison of Amici spectra with model atmospheres allows us to obtain a reliable estimate of the dwarf effective temperatures
- ID:
- ivo://CDS.VizieR/J/ApJ/723/684
- Title:
- NIRSPEC ultracool dwarf radial velocity survey
- Short Name:
- J/ApJ/723/684
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of an infrared Doppler survey designed to detect brown dwarf and giant planetary companions to a magnitude-limited sample of ultracool dwarfs (UCDs). Using the NIRSPEC spectrograph on the Keck II telescope, we obtained approximately 600 radial velocity (RV) measurements over a period of six years of a sample of 59 late-M and L dwarfs spanning spectral types M8/L0 to L6. A subsample of 46 of our targets has been observed on three or more epochs. We rely on telluric CH_4_ absorption features in Earth's atmosphere as a simultaneous wavelength reference and exploit the rich set of CO absorption features found in the K-band spectra of cool stars and brown dwarfs to measure RVs and projected rotational velocities. For a bright, slowly rotating M dwarf standard we demonstrate an RV precision of 50m/s and for slowly rotating L dwarfs we achieve a typical RV precision of approximately 200m/s. This precision is sufficient for the detection of close-in giant planetary companions to mid-L dwarfs as well as more equal mass spectroscopic binary systems with small separations (a<2AU). Using a kinematic age estimate, we conclude that our UCDs have an age of 5.0^+0.7^_-0.6_Gyr, similar to that of nearby sun-like stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/117
- Title:
- NIR stellar populations in Sextans A and Leo A
- Short Name:
- J/ApJ/854/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present JHKs observations of the metal-poor ([Fe/H]{<}-1.40) dwarf-irregular galaxies, Leo A and Sextans A, obtained with the WIYN High-resolution Infrared Camera at Kitt Peak. Their near-IR stellar populations are characterized by using a combination of color-magnitude diagrams and by identifying long-period variable stars. We detected red giant and asymptotic giant branch stars, consistent with membership of the galaxy's intermediate-age populations (2-8Gyr old). Matching our data to broadband optical and mid-IR photometry, we determine luminosities, temperatures, and dust-production rates (DPR) for each star. We identify 32 stars in LeoA and 101 stars in Sextans A with a DPR>10^-11^M_{sun}_/yr, confirming that metal-poor stars can form substantial amounts of dust. We also find tentative evidence for oxygen-rich dust formation at low metallicity, contradicting previous models that suggest oxygen-rich dust production is inhibited in metal-poor environments. The total rates of dust injection into the interstellar medium of Leo A and Sextans A are (8.2+/-1.8)x10^-9^M_{sun}_/yr and (6.2+/-0.2)x10^-7^M_{sun}/yr, respectively. The majority of this dust is produced by a few very dusty evolved stars and does not vary strongly with metallicity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/418/863
- Title:
- NLTE corrections for Mg and Ca lines
- Short Name:
- J/MNRAS/418/863
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate NLTE effects for magnesium and calcium in the atmospheres of late-type giant and supergiant stars. The aim of this paper is to provide a grid of NLTE/LTE equivalent width ratios W/W* of Mg and Ca lines for the following range of stellar parameters: Teff in [3500,5250]K, log(g) in [0.5,2.0]dex and [Fe/H] in [-4.0,0.5]dex. We use realistic model atoms with the best physics available and taking into account the fine structure. The Mg and Ca lines of interest are in optical and near IR ranges. A special interest concerns the lines in the Gaia spectrograph (RVS) wavelength domain [847,874]nm. The NLTE corrections are provided as function of stellar parameters in an electronic table as well as in a polynomial form for the Gaia/RVS lines.
- ID:
- ivo://CDS.VizieR/II/41
- Title:
- 420nm CN and G bands in G8-K5 spectra
- Short Name:
- II/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Measurements of the {lambda}4200{AA} CN band are presented for 712 late-type stars. G band data are also included for 212 of these stars. Mean errors of absolute magnitudes derived from CN intensities are at least 1.5 mag. Spectral type determined by G band intensity has a mean deviation of 0.15 class from the MK type for G to K1 stars. The file photom.dat contains 712 data records in the form of CN ratios and G-band ratios, with annotations. The CN ratio is the ratio of the sum of the intensities in the 4097-4149{AA} and 4230-4283{AA} wavelength ranges to the intensity in the 4164-4214{AA} range. The latter contains the CN absorption band, and the first two ranges serve as nearby continuum references. The ratio is a measure of the depth of the absorption in the CN band. Values greater than 2 indicate absorption in the band. The G-band ratio is similarly the ratio of the sum of the intensities in the 4230-4270{AA} and 4342-4380{AA} wavelength ranges to the intensity in the 4285-4315{AA} range.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A177
- Title:
- Non-LTE analysis of K I in late-type stars
- Short Name:
- J/A+A/627/A177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Older models of Galactic chemical evolution (GCE) predict [K/Fe] ratios as much as 1dex lower than those inferred from stellar observations. Abundances of potassium are mainly based on analyses of the 7698{AA} resonance line, and the discrepancy between GCE models and observations is in part caused by the assumption of local thermodynamic equilibrium (LTE) in spectroscopic analyses. We study the statistical equilibrium of KI, focusing on the non-LTE effects on the 7698{AA} line. We aim to determine how non-LTE abundances of potassium can improve the analysis of its chemical evolution, and help to constrain the yields of GCE models. We construct a new model KI atom that employs the most up-to-date atomic data. In particular, we calculate and present inelastic e+K collisional excitation cross-sections from the convergent close-coupling (CCC) and the B-Spline R-matrix (BSR) methods, and H+K collisions from the two-electron model (LCAO). We constructed a fine, extended grid of non-LTE abundance corrections based on 1D MARCS models that span 4000<Teff/=K<8000, 0.50<logg<5.00, -5.00<[Fe/H]<+0.50, and applied the corrections to potassium abundances extracted from the literature.
- ID:
- ivo://CDS.VizieR/J/ApJ/669/446
- Title:
- Observations of SiO masers
- Short Name:
- J/ApJ/669/446
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of SiO millimeter line observations of a sample of known SiO maser sources covering a wide dust temperature range. A cold part of the sample was selected from the SiO maser sources found in our recent SiO maser survey of cold dusty objects. The aim of the present research is to investigate the causes of the correlation between infrared colors and SiO maser intensity ratios among different transition lines. In particular, the correlation between infrared colors and SiO maser intensity ratio among the J=1-0 v=1, 2, and 3 lines are our main concern in this paper. We observed in total 75 SiO maser sources with the Nobeyama 45m telescope quasi-simultaneously in the SiO J=1-0 v=0, 1, 2, 3, 4 and J=2-1 v=1, 2 lines. We also observed the sample in the ^29^SiO J=1-0 v=0 and J=2-1 v=0 lines, ^30^SiO J=1-0 v=0 line, and the H_2_O 61,6-52,3 line.
- ID:
- ivo://CDS.VizieR/J/A+A/394/975
- Title:
- OH 5-cm line survey in late-type stars
- Short Name:
- J/A+A/394/975
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have undertaken a comprehensive search for 5-cm excited OH maser emission from evolved stars representative of various stages of late stellar evolution. Observed sources were selected from known 18-cm OH sources. This survey was conducted with the 100-m Effelsberg telescope, at 6.0GHz in Sep 2000, to achieve high signal to noise ratio observations and a sensitivity limit of about 0.05 to 0.1Jy. A total of 65 stellar sources were searched for both main line and satellite line emission. We confirm the previous detection of 5 cm OH in Vy 2-2, do not confirm emission from NML-Cyg and do not report any other new detection within the above sensitivity limit. The number of observed sources is 67.
