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1561. M dwarfs HeI infrared triplet variability
ID:
ivo://CDS.VizieR/J/A+A/640/A52
Title:
M dwarfs HeI infrared triplet variability
Short Name:
J/A+A/640/A52
Date:
21 Oct 2021
Publisher:
CDS
Description:
The HeI infrared (IR) triplet at 10830{AA} is an important activity indicator for the Sun and in solar-type stars, however, it has rarely been studied in relation to M dwarfs to date. In this study, we use the time-averaged spectra of 319 single stars with spectral types ranging from M0.0 V to M9.0V obtained with the CARMENES high resolution optical and near-infrared spectrograph at Calar Alto to study the properties of the HeI IR triplet lines. In quiescence, we find the triplet in absorption with a decrease of the measured pseudo equivalent width (pEW) towards later sub-types. For stars later than M5.0 V, the HeI triplet becomes undetectable in our study. This dependence on effective temperature may be related to a change in chromospheric conditions along the Mdwarf sequence. When an emission in the triplet is observed, we attribute it to flaring. The absence of emission during quiescence is consistent with line formation by photo-ionisation and recombination, while flare emission may be caused by collisions within dense material. The HeI triplet tends to increase in depth according to increasing activity levels, ultimately becoming filled in; however, we do not find a correlation between the pEW(He IR) and X-ray properties. This behaviour may be attributed to the absence of very inactive stars (LX/Lbol<-5.5) in our sample or to the complex behaviour with regard to increasing depth and filling in.
1562. 3 M dwarfs near-infrared spectra
ID:
ivo://CDS.VizieR/J/A+A/542/A33
Title:
3 M dwarfs near-infrared spectra
Short Name:
J/A+A/542/A33
Date:
21 Oct 2021
Publisher:
CDS
Description:
The relatively large spread in the derived metallicities ([Fe/H]) of M dwarfs shows that various approaches have not yet converged to consistency. The presence of strong molecular features, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs difficult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio sufficient for a detailed spectroscopic abundance analysis. We present a high-resolution (R~50000) spectroscopic study of a sample of eight single M dwarfs and three wide-binary systems observed in the infrared J-band.
1563. M dwarf SpeX NIR spectroscopy
ID:
ivo://CDS.VizieR/J/ApJ/802/L10
Title:
M dwarf SpeX NIR spectroscopy
Short Name:
J/ApJ/802/L10
Date:
21 Oct 2021
Publisher:
CDS
Description:
Despite the ubiquity of M dwarfs and their growing importance to studies of exoplanets, Galactic evolution, and stellar structure, methods for precisely measuring their fundamental stellar properties remain elusive. Existing techniques for measuring M dwarf luminosity, mass, radius, or composition are calibrated over a limited range of stellar parameters or require expensive observations. We find a strong correlation between the K_S_-band luminosity (M_K_), the observed strength of the I-band sodium doublet absorption feature, and [Fe/H] in M dwarfs without strong H{alpha} emission. We show that the strength of this feature, coupled with [Fe/H] and spectral type, can be used to derive M dwarf M_K_ and radius without requiring parallax. Additionally, we find promising evidence that the strengths of the I-band sodium doublet and the nearby I-band calcium triplet may jointly indicate {alpha}-element enrichment. The use of these I-band features requires only moderate-resolution near-infrared spectroscopy to provide valuable information about the potential habitability of exoplanets around M dwarfs, and surface gravity and distance for M dwarfs throughout the Galaxy. This technique has immediate applicability for both target selection and candidate planet-host system characterization for exoplanet missions such as TESS and K2.
1564. Mean galaxy spectra of the 86 classes
ID:
ivo://CDS.VizieR/J/A+A/649/A53
Title:
Mean galaxy spectra of the 86 classes
Short Name:
J/A+A/649/A53
Date:
22 Feb 2022
Publisher:
CDS
Description:
Defining templates of galaxy spectra is useful to quickly characterise new obervations and organise data bases from surveys. These templates are usually built from a pre-defined classification based on other criteria. We present an unsupervised classification of 702248 spectra of galaxies and quasars with redshifts smaller than 0.25 that were retrieved from the Sloan Digital Sky Survey (SDSS) database, release 7. The spectra were first corrected for the redshift, then wavelet-filtered to reduce the noise, and finally binned to obtain about 1437 wavelengths per spectrum. Fisher-EM, an unsupervised clustering discriminative latent mixture model algorithm, was applied on these corrected spectra, considering the full set as well as several subsets of 100000 and 300000 spectra. The optimum number of classes given by a penalised likelihood criterion is 86 classes, the 37 most populated ones gathering 99% of the sample. These classes are established from a subset of 302214 spectra. Using several cross-validation techniques we find that this classification is in agreement with the results obtained on the other subsets with an average misclassification error of about 15\%. The large number of very small classes tends to increase this error rate. In this paper, we make a first quick comparison of our classes with the templates of Kennicutt (1992), Dobos et al (2012), Wang et al (2018). This is the first time that an automatic, objective and robust unsupervised classification is established on such a large amount of spectra of galaxies. The mean spectra of the classes can be used as templates for a large majority of galaxies in our Universe.
1565. Mean rest-UV spectra of Ly{alpha} emitters at z>3
ID:
ivo://CDS.VizieR/J/A+A/641/A118
Title:
Mean rest-UV spectra of Ly{alpha} emitters at z>3
Short Name:
J/A+A/641/A118
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the ultraviolet (UV) spectral properties of faint Lyman{alpha} emitters (LAEs) in the redshift range 2.9<=z<=4.6 and provide material to prepare future observations of the faint Universe. We use data from the MUSE Hubble Ultra Deep Survey to construct mean rest-frame spectra of continuum-faint (median M_UV_ of -18 and down to M_UV_ of -16), low stellar mass (median value of 10^8.4^ and down to 10^7^ solar masses) LAEs at redshift z>3. We compute various averaged spectra of LAEs sub-sampled on the basis of their observational (e.g., Ly{alpha} strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. We search for UV spectral features other than Ly{alpha}, such as higher-ionization nebular emission lines and absorption features. We successfully observe the OIII]{lambda}1666 and [CIII]{lambda}1907+CIII]{lambda}1909 collisionally excited emission lines and the HeII{lambda}1640 recombination feature, as well as the resonant CIV{lambda}1548,1551 doublet either in emission or P-Cygni. We compare the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Ly{alpha} equivalent widths, fainter UV magnitudes, bluer UV spectral slopes and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in individual spectra of z>2 galaxies. This suggests that weak UV features are likely ubiquitous in high z, low-mass and faint LAEs. We publicly release the stacked spectra as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope.
1566. Mean Spectra for upper AGB stars
ID:
ivo://CDS.VizieR/J/A+A/393/167
Title:
Mean Spectra for upper AGB stars
Short Name:
J/A+A/393/167
Date:
21 Oct 2021
Publisher:
CDS
Description:
Provided are average spectra extending from 510 to 2490nm for: - Oxygen rich, optically visible LPVs (temperature sequence based on the colour I-K); - Carbon rich, optically visible LPVs (temperature sequence based on the colour R-H, and C/O sequence); - Oxygen rich, dust-enshrouded LPVs (reddened versions of the coolest optically visible average); - Carbon rich, dust-enshrouded LPVs (reddened versions of the coolest optically visible average).
1567. Mean spectrum of CP Pup in 1996
ID:
ivo://CDS.VizieR/J/A+A/539/A94
Title:
Mean spectrum of CP Pup in 1996
Short Name:
J/A+A/539/A94
Date:
21 Oct 2021
Publisher:
CDS
Description:
CP Pup (Nova Pup 1942) showed outburst and quiescent characteristics indicating a very massive white dwarf, yet the standard spectroscopic dynamical analysis assuming an accretion disk yields an extremely low value for the white dwarf mass. However, some physical parameters and the accretion geometry are still poorly known. The nova was spectroscopically monitored between 1988 and 1996. We analyzed the whole data set in order to re-determine the spectroscopic period and examine its stability. We also looked for chemical anomalies in the spectrum.
1568. Mean UV Spectra of Stellar Groups
ID:
ivo://CDS.VizieR/J/ApJS/82/197
Title:
Mean UV Spectra of Stellar Groups
Short Name:
J/ApJS/82/197
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a library of mean ultraviolet stellar energy distributions derived from International Ultraviolet Explorer (IUE) low-resolution spectrophotometry of 216 stars. The library is intended to facilitate interpretation of the composite UV light of stellar populations such as star clusters and galaxies. The spectra cover 1205-3185 Angstroms with a spectral resolution of approximately 6 A. The individual stellar spectra were corrected for interstellar extinction (using the Savage-Mathis law), converted to a common flux scale, and interpolated to a common wavelength scale. Stars were combined into standard groups according to their intrinsic continuum colors, observed UV spectral morphology, MK luminosity class, and metal abundance. The library consists of 56 groups: 21 dwarf (V), 8 subgiant (IV), 16 giant (III), and 11 supergiant (I+II) groups, covering O3-M4 spectral types. A metal-poor sequence is included, containing four dwarf and two giant groups, as is a metal-enhanced sequence with a single dwarf, subgiant, and giant group. More information on the library compilation and descriptions of the behaviour of spectral indices characterizing the continuum and strong absorption features are given in the paper. The spectra themselves (in the uvgroups.fit file) were previously released in the AAS CD-ROM Series Volume VII (1996); see Leitherer et al. "A Database for Galaxy Evolution Modeling" (1996PASP..108..996L).
1569. Measured atmospheric parameters of NGC6397 stars
ID:
ivo://CDS.VizieR/J/A+A/635/A161
Title:
Measured atmospheric parameters of NGC6397 stars
Short Name:
J/A+A/635/A161
Date:
21 Oct 2021
Publisher:
CDS
Description:
Recent work has used spectra of ~5000 stars in NGC 6397 that were extracted from a MUSE mosaic to determine the atmospheric parameters for these stars by fitting the spectra against the Goettingen Spectral Library. A significant change in metallicity between the turn off and the red giant branch was found and was discussed as a possible manifestation of predicted effects of atomic diffusion. However, the small amplitude of the effect and inconsistency with earlier measurements call for more attention before this result is interpreted. Systematic effects due to the interpolation or to the synthetic spectra cannot be ruled out at this level of precision. We reanalyze the data with : the ELODIE and MILES reference libraries in order to assess the robustness of the result. These empirical libraries have a finer metallicity coverage down to approximately the cluster metallicity turn-off. Methods. We used the ULySS full-spectrum fitting package, together with the library interpolators to remeasure the three atmospheric parameters effective temperature, surface gravity, and [Fe/H] metallicity. We find a very low [Fe/H] dispersion along the isochrone (0.07dex), consistent with our error estimate (0.05dex). However, the [Fe/H] trend is not reproducible. This shows that the data have the potential to reveal patterns of the magnitude of the expected physical effects, but the analysis methods need to be refined to cull systematic effects that currently dominate the patterns.
1570. MEGaSaURA. II. Stacked spectra
ID:
ivo://CDS.VizieR/J/ApJ/853/87
Title:
MEGaSaURA. II. Stacked spectra
Short Name:
J/ApJ/853/87
Date:
21 Oct 2021
Publisher:
CDS
Description:
We stack the rest-frame ultraviolet spectra of N=14 highly magnified gravitationally lensed galaxies at redshifts 1.6<z<3.6. The resulting new composite spans 900<{lambda}_rest_<3000{AA}, with a peak signal-to-noise ratio (S/N) of 103 per spectral resolution element (~100km/s). It is the highest S/N, highest spectral resolution composite spectrum of z~2-3 galaxies yet published. The composite reveals numerous weak nebular emission lines and stellar photospheric absorption lines that can serve as new physical diagnostics, particularly at high redshift with the James Webb Space Telescope (JWST). We report equivalent widths to aid in proposing for and interpreting JWST spectra. We examine the velocity profiles of strong absorption features in the composite, and in a matched composite of z~0 COS/HST galaxy spectra. We find remarkable similarity in the velocity profiles at z~0 and z~2, suggesting that similar physical processes control the outflows across cosmic time. While the maximum outflow velocity depends strongly on ionization potential, the absorption-weighted mean velocity does not. As such, the bulk of the high- ionization absorption traces the low-ionization gas, with an additional blueshifted absorption tail extending to at least -2000km/s. We interpret this tail as arising from the stellar wind and photospheres of massive stars. Starburst99 models are able to replicate this high-velocity absorption tail. However, these theoretical models poorly reproduce several of the photospheric absorption features, indicating that improvements are needed to match observational constraints on the massive stellar content of star-forming galaxies at z~2.

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