- ID:
- ivo://CDS.VizieR/J/A+AS/111/57
- Title:
- Synthetic absorption in star forming regions
- Short Name:
- J/A+AS/111/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral evolutionary calculations have been employed in order to follow the behaviour of absorption lines in single-burst star forming regions. The model calculations are based on theoretical evolutionary tracks and model atmosphere stellar spectra at 5A resolution and they include the pre-main sequence phase. Three different metallicities have been considered; Z=0.001, 0.008 and 0.020, this range covers easily the one occupied by blue compact dwarf galaxies. This analysis focuses on the post-active burst phase and follows the evolution up to 15 million years after the episode of star formation has ceased, using an instantaneous burst of star formation. The absorption lines included are hydrogen, neutral and once ionized helium. Non-LTE absorption line profiles have been implemented to these lines, also at a 5A resolution. The equivalent widths and line profiles are studied as a function of lower and upper mass limits and slope of the mass function as well as the age. It is shown that the equivalent widths of the Balmer lines are increasing during the course of evolution, while the strength of the neutral and ionized helium lines decreases monotonically. Both the hydrogen and helium lines show high sensitivity to variations in the initial mass function (IMF). The Balmer line equivalent widths range from about 1.5 to 6.5A, depending on the IMF parameters used. As anticipated, these numbers are rather insensitive to the metallicity. Contrary to what has been claimed, the Balmer lines are prominent even if the lower mass limit is as high as 10M_{sun}_. It has been proposed that the weak hydrogen lines sometimes seen in starburst galaxies, often interpreted as evidence for a deficiency in low mass stars, could be due to the finite lifetimes of pre-main sequence stars. This analysis shows that it is very much dependent on the slope of the mass function. The equivalent width of the HeI-4471A line never exceeds 0.35A for any choice of the IMF parameters while the equivalent width of the HeII-4686A line reaches at the most 0.20A using the most top-heavy IMF. As expected, these numbers are only slightly dependent on the metallicity in the optical spectral region.
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21332. Synthetic galaxy spectra
- ID:
- ivo://CDS.VizieR/J/A+A/538/A38
- Title:
- Synthetic galaxy spectra
- Short Name:
- J/A+A/538/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an optimized library of synthetic galaxy spectra that are to be used for the Gaia satellite observations of unresolved galaxies. These galaxy spectral templates are useful for the optimal performance of the unresolved galaxy classifier (UGC) software. The UGC will assign spectral classes to the observed unresolved galaxies by Gaia (classification) and estimate some of their intrinsic astrophysical parameters, which were used to create the synthetic library (parametrization). We present the new optimized synthetic library of galaxy spectra and the classification and parametrization results using the Gaia-simulated version of this library. To optimize our synthetic library, we applied the principal component analysis (PCA) method to our synthetic spectra and studied the influence of the star-formation rate parameters on the spectra, and how these agree with some typical characteristics of the galaxy spectral types. We used support vector machines (SVM) to classify and parametrize the optimal simulated spectra. The library of synthetic galaxy spectra was optimized. In this new set of synthetic spectra, overlaps in spectral energy distributions and colors are highly suppressed, while the results of UGC classification are improved.
- ID:
- ivo://CDS.VizieR/J/A+A/596/A49
- Title:
- Synthetic GALEX photometry for IUE sources
- Short Name:
- J/A+A/596/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galaxy Evolution Explorer (GALEX) has produced the largest photometric catalogue of ultraviolet (UV) sources. As such, it has defined the new standard bands for UV photometry: the near UV band (NUV) and the far UV band (FUV). However, due to brightness limits, the GALEX mission has avoided the Galactic plane which is crucial for astrophysical research and future space missions. The International Ultraviolet Explorer (IUE) satellite obtained 63,755 spectra in the low dispersion mode ({lambda}/{delta}{lambda}~300) during its 18-year lifetime. We have derived the photometry in the GALEX bands for the stellar sources in the IUE Archive to extend the GALEX database with observations including the Galactic plane. Good quality spectra have been selected for the IUE classes of stellar sources. The GALEX FUV and NUV magnitudes have been computed using the GALEX transmission curves, as well as the conversion equations between flux and magnitudes provided by the mission (galexgi.gsfc.nasa.gov). Consistency between GALEX and IUE synthetic photometries has been tested using White Dwarfs (WD) contained in both samples. The non-linear response performance of GALEX inferred from this data agrees with the results from GALEX calibration. The photometric database is made available to the community through the services of the Centre de Donnees Stellaires at Strasbourg (CDS). The catalogue contains FUV magnitudes for 1628 sources, ranging from FUV=1.81 to FUV=18.65mag. In the NUV band, the catalogue includes observations for 999 stars ranging from NUV=3.34 to NUV=17.74mag. UV photometry for 1490 sources not included in the GALEX AIS GR5 catalogue is provided; most of them are hot (O-A spectral type) stars. The sources in the catalogue are distributed over the full sky, including the Galactic plane.
- ID:
- ivo://CDS.VizieR/J/ApJ/841/15
- Title:
- Synthetic JWST/MIRI fluxes and magnitudes
- Short Name:
- J/ApJ/841/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Mid-Infrared Instrument (MIRI) for the James Webb Space Telescope (JWST) will revolutionize our understanding of infrared stellar populations in the Local Volume. Using the rich Spitzer-IRS spectroscopic data set and spectral classifications from the Surveying the Agents of Galaxy Evolution (SAGE)-Spectroscopic survey of more than 1000 objects in the Magellanic Clouds, the Grid of Red Supergiant and Asymptotic Giant Branch Star Model (GRAMS; Sargent+ 2011ApJ...728...93S and Srinivasan+ 2011, J/A+A/532/A54), and the grid of YSO models by Robitaille+ (2006ApJS..167..256R), we calculate the expected flux densities and colors in the MIRI broadband filters for prominent infrared stellar populations. We use these fluxes to explore the JWST/MIRI colors and magnitudes for composite stellar population studies of Local Volume galaxies. MIRI color classification schemes are presented; these diagrams provide a powerful means of identifying young stellar objects, evolved stars, and extragalactic background galaxies in Local Volume galaxies with a high degree of confidence. Finally, we examine which filter combinations are best for selecting populations of sources based on their JWST colors.
- ID:
- ivo://CDS.VizieR/J/ApJ/601/485
- Title:
- Synthetic Lick indices of alpha-enhanced stars
- Short Name:
- J/ApJ/601/485
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Synthetic Lick indices computed with solar scaled abundances and with {alpha}-element enhancement are presented and compared with predictions from both theoretical computations (Tripicco & Bell (1995AJ....110.3035T); Thomas, Maraston, & Bender (2003MNRAS.339..897T); Barbuy et al., 2003, Cat. <J/A+A/404/661>) and empirical fitting functions (de Freitas Pacheco, 1996MNRAS.278..841D). We propose selected combinations of indices capable of singling out {alpha}-enhanced stars without requiring previous knowledge of their main atmospheric parameters. By applying this approach to the 460 stars in the Worthey et al. (1994, Cat. <J/ApJS/94/687>) catalog, we detected a list of 82 candidate {alpha}-enhanced stars. The confirmation of {alpha}-enhancement was obtained by searching the literature for individual element abundance determinations from high-resolution spectroscopy for a subsample of 34 stars. Preliminary discussion of the properties of the detected {alpha}-enhanced stars with respect to their [Fe/H] values and kinematics is presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/634/1319
- Title:
- Synthetic Lick indices of alpha-enhanced stars
- Short Name:
- J/ApJ/634/1319
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of 119 F, G, and K solar neighborhood stars, selected under the condition [Fe/H]>0.00, is investigated in order to detect which of them, if any, present {alpha}-enhanced characteristics. According to the kinematics, the sample represents stars of the thin-disk component of the Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/613/312
- Title:
- Synthetic Lick indices of alpha-enhanced stars
- Short Name:
- J/ApJ/613/312
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of 402 F, G, and K solar neighborhood stars, with accurate estimates of [Fe/H] in the range -1.0 to +0.5dex, aimed at the detection of {alpha}-enhanced stars and at the investigation of their kinematical properties. The analysis is based on the comparison of 571 sets of spectral indices in the Lick/IDS system, coming from four different observational data sets, with synthetic indices computed with solar-scaled abundances and with {alpha}-element enhancement. We use selected combinations of indices to single out {alpha}-enhanced stars without requiring previous knowledge of their main atmospheric parameters. By applying this approach to the total data set, we obtain a list of 60 bona fide {alpha}-enhanced stars and of 146 stars with solar-scaled abundances. The properties of the detected {alpha}-enhanced and solar-scaled abundance stars with respect to their [Fe/H] values and kinematics are presented. A clear kinematic distinction between solar-scaled and {alpha}-enhanced stars was found, although a one-to-one correspondence to "thin disk" and "thick disk" components cannot be supported with the present data.
21338. Synthetic lines in the Sun
- ID:
- ivo://CDS.VizieR/J/A+A/528/A113
- Title:
- Synthetic lines in the Sun
- Short Name:
- J/A+A/528/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have computed synthetic spectra from a realistic 3D numerical simulation of the solar photosphere. We provide the spatially averaged spectra for selected lines that are commonly used on solar applications. These data can be used to calibrate Doppler velocity measurements in the solar photosphere. The calculations are carried out along the solar disk from heliocentric angle mu=1.0 to mu=0.3.
- ID:
- ivo://CDS.VizieR/J/ApJ/657/1046
- Title:
- Synthetic Mid-UV spectroscopic indices of stars
- Short Name:
- J/ApJ/657/1046
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the UVBLUE library of synthetic stellar spectra we have computed a set of mid-UV line and continuum spectroscopic indices. We explore their behavior in terms of the leading stellar parameters (Teff, logg). The overall result is that synthetic indices follow the general trends depicted by those computed from empirical databases. Separately we also examine the index sensitivity to changes in chemical composition, an analysis only feasible under a theoretical approach. In this respect, lines indices FeI 3000, BL 3096, and MgI 2852 and the continuum index 2828/2921 are the least sensitive features, an important characteristic to be taken into account for the analyses of integrated spectra of stellar systems.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A9
- Title:
- Synthetic photometry as a function of redshift
- Short Name:
- J/A+A/633/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the spectral properties of proto-GCs that would host a supermassive star (SMS). Our main goal is to quantify how such a star would affect the integrated light of the cluster, and to study the detectability of such objects. We computed nonlocal thermal equilibrium atmosphere models for SMS with various combinations of stellar parameters (luminosity, effective temperature, and mass) and metallicities appropriate for GCs, and we predict their emergent spectra. Using these spectra, we calculated the total emission of young proto-GCs with SMS as predicted in a previously reported scenario, and we computed synthetic photometry in UV, optical, and near-IR bands, in particular for the James Webb Space Telescope (JWST). At an effective temperature of 10000K, the spectrum of SMSs shows a Balmer break in emission. This feature is due to strong nonlocal thermal equilibrium effects (implied by the high luminosity) and is not observed in "normal" stars. The hydrogen lines also show a peculiar behavior, with Balmer lines in emission while higher series lines are in absorption. At 7000 K, the Balmer break shows a strong absorption. At high effective temperatures, the Lyman break is found in emission. Cool and luminous SMSs are found to dominate the integrated spectrum of the cluster, except for the UV range. The predicted magnitudes of these proto-GCs are mag_AB_~28-30 between 0.7 and 8um and for redshifts z~4-10, which is detectable with the JWST. The peculiar observational features of cool SMSs imply that they might in principle be detected in color-color diagrams that probe the spectral energy distribution below and above the Balmer break.
