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1841. NLTE spectral analysis of white dwarf G191-B2B
ID:
ivo://CDS.VizieR/J/A+A/560/A106
Title:
NLTE spectral analysis of white dwarf G191-B2B
Short Name:
J/A+A/560/A106
Date:
21 Oct 2021
Publisher:
CDS
Description:
Hydrogen-rich, DA-type white dwarfs are particularly suited as primary standard stars for flux calibration. State-of-the-art NLTE models consider opacities of species up to trans-iron elements and provide reliable synthetic stellar-atmosphere spectra to compare with observation. We will establish a database of theoretical spectra of stellar flux standards that are easily accessible via a web interface.
1842. 540-690nm Solar Atlas
ID:
ivo://CDS.VizieR/J/A+A/525/A74
Title:
540-690nm Solar Atlas
Short Name:
J/A+A/525/A74
Date:
21 Oct 2021
Publisher:
CDS
Description:
Astronomical research dealing with accurate radial velocity measurements need reliable astronomical standards to calibrate the spectrographs and to assess possible systematics. Stellar radial velocity standards offer a reference at the level of a few hundred m/s and are not adequate for most present needs. We aim to show that sunlight reflected by asteroids is a fairly accessible way to record a high-resolution solar spectrum from the whole disk, which can therefore be used as a radial velocity standard and can improve the uncertainties of solar line positions.
1843. 398-710nm Sun spectral atlases
ID:
ivo://CDS.VizieR/J/other/ApSS/353.347
Title:
398-710nm Sun spectral atlases
Short Name:
J/other/ApSS/353
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this work, we present digital and graphical atlases of spectra of both the solar disk-center and of the limb near the Solar poles using data taken at the UTS-IAP & RIAAM (the University of Tabriz Siderostat, telescope and spectrograph jointly developed with the Institut d'Astrophysique de Paris and Research Institute for Astronomy and Astrophysics of Maragha). High resolution and high signal-to-noise ratio (SNR) CCD-slit spectra of the sun for 2 different parts of the disk, namely for {mu}=1.0 (solar center) & for {mu}=0.3 (solar limb) are provided and discussed. While there are several spectral atlases of the solar disk-center, this is the first spectral atlas ever produced for the solar limb at this spectral range. The resolution of the spectra is about R~70000 ({Delta}{lambda}~0.09{AA})} with the signal-to-noise ratio (SNR) of 400-600. The full atlas covers the 3980 to 7100{AA} spectral regions and contains 44 pages with three partial spectra of the solar spectrum put on each page to make it compact. The difference spectrum of the normalized each page to make it compact. The difference spectrum of the normalized solar disk-center and the solar limb is also included in the graphic presentation of the atlas to show the difference of line profiles, including far wings. The identification of most of the significant solar lines are included in the graphic presentation of the atlas. Telluric lines are producing a definite signature on the difference spectra which is easy to notice.
1844. N66, N88 & N25+N26 emission line maps
ID:
ivo://CDS.VizieR/J/A+A/589/A28
Title:
N66, N88 & N25+N26 emission line maps
Short Name:
J/A+A/589/A28
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents [CII], [CI] and CO emission line maps of the star-forming regions N66, N25+N26, and N88 in the metal-poor Local Group dwarf galaxy SMC. The spatial and velocity structure of the large HII region N66 reveals an expanding ring of shocked molecular gas centered on the exciting star cluster NGC346, whereas a more distant dense molecular cloud is being eroded by UV radiation from the same cluster. In the N25+N26 and N88 maps, diffuse [CII] emission at a relatively low surface brightness extends well beyond the compact boundaries of the bright emission associated with the HII regions. In all regions, the distribution of this bright [CII] emission and the less prominent [CI] emission closely follows the outline of the CO complexes, but the intensity of the [CII] and [CI] emission is generally anticorrelated, which can be understood by the action of photodissociation and photoionization processes. Notwithstanding the overall similarity of CO and [CII] maps, the intensity ratio of these lines varies significantly, mostly due to changes in CO brightness. [CII] emission line profiles are up to 50% wider in velocity than corresponding CO profiles. A radiative transfer analysis shows that the [CII] line is the dominant tracer of (CO-dark) molecular hydrogen in the SMC. CO emission traces only a minor fraction of the total amount of gas. The similarity of the spatial distribution and line profile shape, and the dominance of molecular gas associated with CII rather than CO emission imply that in the low-metallicity environment of the SMC the small amount of dense molecular gas traced by CO is embedded in the much more extended molecular gas traced only by [CII] emission. The contribution from neutral atomic and ionized hydrogen zones is negligible in the star-forming regions observed
1845. 14N/15N ratio in YSOs
ID:
ivo://CDS.VizieR/J/A+A/644/A29
Title:
14N/15N ratio in YSOs
Short Name:
J/A+A/644/A29
Date:
21 Oct 2021
Publisher:
CDS
Description:
The nitrogen isotopic ratio is considered an important diagnostic tool of the star formation process, and N_2_H^+^ is particularly important because it is directly linked to molecular nitrogen N_2_. However, theoretical models still lack to provide an exhaustive explanation for the observed^14^N/^15^N values. Recent theoretical works suggest that the^14^N/^15^N behaviour is dominated by two competing reactions that destroy N_2_H^+^: dissociative recombination and reaction with CO. When CO is depleted from the gas phase, if N_2_H^+^ recombination rate is lower with respect to the N^15^NH^+^ one, the rarer isotopologue is destroyed faster. In prestellar cores, due to a combination of low temperatures and high densities, most CO is frozen in ices onto the dust grains, leading to high levels of depletion. On the contrary, in protostellar cores, where temperature are higher, CO ices evaporate back to the gas phase. This implies that the N_2_H^+^ isotopic ratio in protostellar cores should be lower than the one in prestellar cores, and consistent with the elemental value of ~440. We aim to test this hypothesis, producing the first sample of N_2_H^+^ /N^15^NH^+^ measurements in low mass protostars. We observe the N_2_H^+^ and N^15^NH^+^ lowest rotational transition towards six young stellar objects in Perseus and Taurusmolecular clouds. We model the spectra with a custom python code using a constant T_ex_ approach to fit the observations. We discuss in appendix the validity of this hypothesis. The derived column densities are used to compute the nitrogen isotopic ratios. Our analysis yields an average of^14^N/^15^N|_pro_=420+/-15 in the protostellar sample. This is consistent with the protosolar value of 440, and significantly lower than the average value previously obtained in a sample of prestellar objects. Our results are in agreement with the hypothesis that, when CO is depleted from the gas-phase, dissociative recombinations with free electrons destroy N^15^NH^+^ faster than N_2_H^+^ , leading to high isotopic ratios in prestellar cores, where carbon monoxide is frozen onto dust grains.
1846. N/O and Ne/O ratios of SDSS dwarf galaxies
ID:
ivo://CDS.VizieR/J/ApJ/864/144
Title:
N/O and Ne/O ratios of SDSS dwarf galaxies
Short Name:
J/ApJ/864/144
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study how the void environment affects the chemical evolution of galaxies in the universe by comparing the oxygen and nitrogen abundances of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, we estimate the oxygen, nitrogen, and neon abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser regions. We use the Direct T_e_ method for calculating the gas-phase chemical abundances in the dwarf galaxies because it is best suited for low-metallicity, low-mass (dwarf) galaxies. A substitute for the [OII]{lambda}3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the Direct T_e_ method. We find that void dwarf galaxies have about the same oxygen abundance and Ne/O ratio as dwarf galaxies in denser environments. However, we find that void dwarf galaxies have slightly higher neon (~10%) abundances than dwarf galaxies in denser environments. The opposite trend is seen in both the nitrogen abundance and N/O ratio: void dwarf galaxies have slightly lower nitrogen abundances (~5%) and lower N/O ratios (~7%) than dwarf galaxies in denser regions. Therefore, we conclude that the void environment has a slight influence on dwarf galaxy chemical evolution. Our mass-N/O relationship shows that the secondary production of nitrogen commences at a lower stellar mass in void dwarf star-forming galaxies than in dwarf star-forming galaxies in denser environments. We also find that star-forming void dwarf galaxies have higher HI masses than the star-forming dwarf galaxies in denser regions. Our star-forming dwarf galaxy sample demonstrates a strong anti-correlation between the sSFR and N/O ratio, providing evidence that oxygen is produced in higher-mass stars than those which synthesize nitrogen. The lower N/O ratios and smaller stellar mass for secondary nitrogen production seen in void dwarf galaxies may indicate both delayed star formation as predicted by {Lambda}CDM cosmology and a dependence of cosmic downsizing on the large-scale environment. A shift toward slightly higher oxygen abundances and higher HI masses in void dwarf galaxies could be evidence of larger ratios of dark matter halo mass to stellar mass in voids compared with denser regions.
1847. NOEMA redshift of bright Herschel galaxies
ID:
ivo://CDS.VizieR/J/A+A/635/A7
Title:
NOEMA redshift of bright Herschel galaxies
Short Name:
J/A+A/635/A7
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we have conducted a program to measure redshifts for thirteen bright galaxies detected in the Herschel Astrophysical Large Area Survey (H-ATLAS) with S(500)>=80mJy. We report reliable spectroscopic redshifts for twelve individual sources, which are derived from scans of the 3 and 2-mm bands, covering up to 31GHz in each band, and are based on the detection of at least two emission lines. The spectroscopic redshifts are in the range between 2.08<z<4.05 with a median value of z=2.9+/-0.6. The sources are unresolved or barely resolved on scales of 10kpc. In one field, two galaxies with different redshifts were detected. In two cases, the sources are found to be binary galaxies with projected distances of ~140kpc. The linewidths of the sources are large, with a mean value for the full width at half maximum of 700+/-300km/s and a median of 800km/s. We analyze the nature of the sources with currently available ancillary data to determine if they are lensed or hyper-luminous (LFIR>10^13^L_{sun}_) galaxies. We also present a re-analysis of the spectral energy distributions including the continuum flux densities measured at 3 and 2-mm to derive overall properties of the sources. Future prospects based on these efficient measurements of redshifts of high-z galaxies using NOEMA are outlined, including a comprehensive survey of all the brightest Herschel galaxies.
1848. NOFS astrometric measurements for distant WDs
ID:
ivo://CDS.VizieR/J/ApJS/239/26
Title:
NOFS astrometric measurements for distant WDs
Short Name:
J/ApJS/239/26
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station between 1989 and 2017, and the average uncertainty in the parallax values is 0.6mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric data set that spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for 19 stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a subsample of 179 white dwarfs (WDs) at distances of 25-200pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass, and cooling age of each WD. Twenty-six WDs are newly classified, and 12 systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of <8Gyr and masses close to the canonical 0.6M_{sun}_.
1849. N/O ratio of dwarf galaxies from SDSS
ID:
ivo://CDS.VizieR/J/ApJ/837/42
Title:
N/O ratio of dwarf galaxies from SDSS
Short Name:
J/ApJ/837/42
Date:
21 Oct 2021
Publisher:
CDS
Description:
We examine how the cosmic environment affects the chemical evolution of galaxies in the universe by comparing the N/O ratio of dwarf galaxies in voids with that of dwarf galaxies in denser regions. Ratios of the forbidden [OIII] and [SII] transitions provide estimates of a region's electron temperature and number density. We estimate the abundances of oxygen and nitrogen using these temperature and density estimates and the emission-line fluxes [OII]3727, [OIII]4959,5007, and [NII]6548,6584 with the direct T_e_ method. Using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, we are able to estimate the N/O ratio in 42 void dwarf galaxies and 89 dwarf galaxies in denser regions. The N/O ratio for void dwarfs (M_r_>-17) is slightly lower (~12%) than for dwarf galaxies in denser regions. We also estimate the nitrogen and oxygen abundances of 2050 void galaxies and 3883 galaxies in denser regions with M_r_>-20. These somewhat brighter galaxies (but still fainter than L_*_) also display similar minor shifts in the N/O ratio. The shifts in the average and median element abundance values in all absolute magnitude bins studied are in the same direction, suggesting that the large-scale environment may influence the chemical evolution of galaxies. We discuss possible causes of such a large-scale environmental dependence of the chemical evolution of galaxies, including retarded star formation and a higher ratio of dark matter halo mass to stellar mass in void galaxies.
1850. Normalized Halpha line profiles of FGK stars
ID:
ivo://CDS.VizieR/J/A+A/624/A10
Title:
Normalized Halpha line profiles of FGK stars
Short Name:
J/A+A/624/A10
Date:
21 Oct 2021
Publisher:
CDS
Description:
The determination of stellar effective temperature (T_eff_) in F, G, and K stars using Halpha profile fitting is a quite remarkable and powerful tool because it does not depend on reddening and is only slightly sensitive to other atmospheric parameters. Nevertheless, this technique is not frequently used because of the complex procedure needed to recover the profile of broad lines in echelle spectra. As a consequence, tests performed on different models have sometimes provided ambiguous results. The main aim of this work is to test the ability of the Halpha profile fitting technique to derive T_eff. We also aim to improve the applicability of this technique to echelle spectra and to test how well 1D+LTE models perform on a variety of F-K stars. We also apply the technique to HARPS spectra and test the reliability and the stability of the HARPS response over several years using the Sun. We have developed a normalization method for recovering undistorted Halpha profiles and we have first applied it to spectra acquired with the single-order coude instrument (resolution R=45000) at do Pico dos Dias Observatory to avoid the problem of blaze correction. The continuum location around Halpha is optimised using an iterative procedure, where the identification of minute telluric features is performed. A set of spectra was acquired with the MUSICOS echelle spectrograph (R=40000) to independently validate the normalization method. The accuracy of the method and of the 1D+LTE model is determined using coude/HARPS/MUSICOS spectra of the Sun and coude-only spectra of a sample of ten Gaia Benchmark Stars with T_eff_ determined from interferometric measurements. HARPS, coude, and MUSICOS spectra are used to determine T_eff_ of 43 sample stars. We find that a proper choice of spectral windows of fits plus the identification of telluric features allow for a very careful normalization of the spectra and produce reliable H{alpha} profiles. We also find that the most used solar atlases cannot be used as templates for Halpha temperature diagnostics without renormalization. The comparison with the Sun shows that H{alpha} profiles from 1D+LTE models underestimate the solar T_eff_ by 28K. We find the same agreement between Halpha and interferometry and between Halpha and Infrared Flux Method: a shallow dependency on metallicity according to the relation T_eff_=T_eff_^Halpha^-159[Fe/H]+28K within the metallicity range -0.70 to +0.40dex. The comparison with the Infrared Flux Method shows a scatter of 59K dominated by photometric errors (52K). In order to investigate the origin of this dependency, we analysed spectra from 3D models and found that they produce hotter temperatures, and that their use largely improves the agreement with the interferometric and Infrared Flux Method measurements. Finally, we find HARPS spectra to be fully suitable for Halpha profile temperature diagnostics; they are perfectly compatible with the coude spectra, and lead to the same T_eff_ for the Sun as that found when analysing HARPS spectra over a timespan of more than 7 years.

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