- ID:
- ivo://CDS.VizieR/J/ApJS/202/17
- Title:
- Far-UV spectral atlas of O-type stars
- Short Name:
- J/ApJS/202/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present a spectral atlas covering the wavelength interval 930-1188{AA} for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188{AA}. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas (Cat. J/ApJS/186/175), to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra.
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- ID:
- ivo://CDS.VizieR/J/ApJ/749/157
- Title:
- Far-UV spectra of Galactic corona sight lines
- Short Name:
- J/ApJ/749/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the properties of the transition temperature (T~10^5^K) gas in the Milky Way corona, based on the measurements of OVI, NV, CIV, SiIV, and FeIII absorption lines seen in the far-ultraviolet spectra of 58 sight lines to extragalactic targets, obtained with the Far-Ultraviolet Spectroscopic Explorer and the Space Telescope Imaging Spectrograph. In many sight lines the Galactic absorption profiles show multiple components, which are analyzed separately. We find that the highly ionized atoms are distributed irregularly in a layer with a scale height of about 3 kpc, which rotates along with the gas in the disk, without an obvious gradient in the rotation velocity away from the Galactic plane. Within this layer the gas has randomly oriented velocities with a dispersion of 40-60km/s. On average the integrated column densities are logN(OVI)=14.3, logN(NV)=13.5, logN(CIV)=14.2, logN(SiIV)=13.6, and logN(FeIII)=14.2, with a dispersion of just 0.2 dex in each case. In sight lines around the Galactic center and Galactic north pole, all column densities are enhanced by a factor ~2, while at intermediate latitudes in the southern sky there is a deficit in N(O VI) of about a factor of two, but no deficit for the other ions.
- ID:
- ivo://CDS.VizieR/J/A+A/553/A126
- Title:
- Far-UV spectra of PN central stars
- Short Name:
- J/A+A/553/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The occurrence of stellar wind in the central star of a planetary nebula (CSPN) can be revealed by the presence of P Cygni profiles of high-excitation lines overimposed on its stellar continuum. We have examined the entire Far-Ultraviolet Spectroscopic Explorer FUSE archive and merged all useful spectroscopic observations of CSPNe to produce the highest quality spectra that can be used to assess the occurrence of stellar winds. Furthermore, the individual spectra of each CSPN have been compared to search for variability in the P Cygni profile. P Cygni profiles of high-excitation lines have been found in 44 CSPNe, with a clear correlation between the ionization potential of the lines and the effective temperature of the star.
- ID:
- ivo://CDS.VizieR/J/ApJS/186/175
- Title:
- Far-UV spectroscopic atlas of B stars
- Short Name:
- J/ApJS/186/175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have constructed a detailed spectral atlas covering the wavelength region 930-1225{AA} for 10 sharp-lined B0-B9 stars near the main sequence. Most of the spectra we assembled are from the archives of the Far Ultraviolet Spectroscopic Explorer satellite, but for nine stars, wavelength coverage above 1188{AA} was taken from high-resolution International Ultraviolet Explorer or echelle Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra. To represent the tenth star at type B0.2V, we used the Copernicus atlas of tau Sco. We made extensive line identifications in the region 949-1225{AA} of all atomic features having published oscillator strengths at types B0, B2, and B8. These are provided as a supplementary data product-hence the term detailed atlas. Our list of found features totals 2288, 1612, and 2469 lines, respectively. We were able to identify 92%, 98%, and 98% of these features with known atomic transitions with varying degrees of certainty in these spectra. The remaining lines do not have published oscillator strengths. Photospheric lines account for 94%, 87%, and 91%, respectively, of all our identifications, with the remainder being due to interstellar (usually molecular H2) lines. We also discuss the numbers of lines with respect to the distributions of various ions for these three most studied spectral subtypes. A table is also given of 162 least blended lines that can be used as possible diagnostics of physical conditions in B star atmospheres.
- ID:
- ivo://CDS.VizieR/J/ApJ/744/121
- Title:
- Far-UV spectroscopy of T Tau stars
- Short Name:
- J/ApJ/744/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a far-ultraviolet (FUV) spectral atlas consisting of spectra of 91 pre-main-sequence stars. Most stars in this sample were observed with the Space Telescope Imaging Spectrograph and Advanced Camera for Surveys on the Hubble Space Telescope (HST). A few archival spectra from the International Ultraviolet Explorer and the Goddard High Resolution Spectrograph on HST are included for completeness. We find strong correlations among the OI{lambda}1304 triplet, the SiIV {lambda}{lambda}1394/1403 doublet, the CIV{lambda}1549 doublet, and the HeII {lambda}1640 line luminosities. For classical T Tauri stars (CTTSs), we also find strong correlations between these lines and the accretion luminosity, suggesting that these lines form in processes related to accretion. These FUV line fluxes and X-ray luminosity correlate loosely with large scatters. The FUV emission also correlates well with H{alpha}, H{beta}, and CaII K line luminosities. These correlations between FUV and optical diagnostics can be used to obtain rough estimates of FUV line fluxes from optical observations. Molecular hydrogen (H_2_) emission is generally present in the spectra of actively accreting CTTSs but not the weak-lined T Tauri stars that are not accreting. The presence of H_2_ emission in the spectrum of HD 98800N suggests that the disk should be classified as actively accreting rather than a debris disk.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/53
- Title:
- Fe-group elemental abundance analysis in HD84937
- Short Name:
- J/ApJ/817/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived new, very accurate abundances of the Fe-group elements Sc through Zn (Z=21-30) in the bright main-sequence turnoff star HD84937 based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD84937 to yield abundance ratios of high precision. The abundances have been determined from both neutral and ionized transitions, which generally are in agreement with each other. We find no substantial departures from the standard LTE Saha ionization balance in this [Fe/H]=-2.32 star. Noteworthy among the abundances are [Co/Fe]=+0.14 and [Cu/Fe]=-0.83, in agreement with past studies of abundance trends in this and other low-metallicity stars, and <[Sc,Ti,V/Fe]>=+0.31 which has not been noted previously. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys reveals that they are positively correlated in stars with [Fe/H]<-2; HD84937 lies at the high end of this correlation. These trends constrain the synthesis mechanisms of Fe-group elements. We also examine the Galactic chemical evolution abundance trends of the Fe-group elements, including a new nucleosynthesis model with jet-like explosion effects.
- ID:
- ivo://CDS.VizieR/J/ApJ/895/78
- Title:
- [Fe/H] and [{alpha}/Fe] in M31 dwarf galaxies
- Short Name:
- J/ApJ/895/78
- Date:
- 15 Mar 2022 06:34:41
- Publisher:
- CDS
- Description:
- We present chemical abundances of red giant branch (RGB) stars in the dwarf spheroidal (dSph) satellite system of Andromeda (M31), using spectral synthesis of medium-resolution (R~6000) spectra obtained with the KeckII telescope and Deep Imaging Multi-Object Spectrometer spectrograph via the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey. We coadd stars according to their similarity in photometric metallicity or effective temperature to obtain a signal-to-noise ratio (S/N) high enough to measure average [Fe/H] and [{alpha}/Fe] abundances. We validate our method using high S/N spectra of RGB stars in Milky Way globular clusters, as well as deep observations for a subset of the M31 dSphs in our sample. For this set of validation coadds, we compare the weighted average abundance of the individual stars with the abundance determined from the coadd. We present individual and coadded measurements of [Fe/H] and [{alpha}/Fe] for stars in 10 M31 dSphs, including the first [{alpha}/Fe] measurements for And IX, XIV, XV, and XVIII. These fainter, less massive dSphs show declining [{alpha}/Fe] relative to [Fe/H], implying an extended star formation history (SFH). In addition, these dSphs also follow the same mass-metallicity relation found in other Local Group satellites. The conclusions we infer from coadded spectra agree with those from previous measurements in brighter M31 dSphs with individual abundance measurements, as well as conclusions from photometric studies. These abundances greatly increase the number of spectroscopic measurements of the chemical composition of M31's less massive dwarf satellites, which are crucial to understanding their SFH and interaction with the M31 system.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/225
- Title:
- -2.6<=[Fe/H]<=0.2 F and G dwarfs. II. Abundances
- Short Name:
- J/ApJ/833/225
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the first time, we present an extensive study of stars with individual non-LTE (NLTE) abundances for 17 chemical elements from Li to Eu in a sample of stars uniformly distributed over the -2.62<=[Fe/H]<=+0.24 metallicity range that is suitable for the Galactic chemical evolution research. The star sample has been kinematically selected to trace the Galactic thin and thick disks and halo. We find new results and improve earlier ones as follows: (i) the element-to-iron ratios for Mg, Si, Ca, and Ti form a metal-poor (MP) plateau at a similar height of 0.3 dex, and the knee occurs at common [Fe/H]~-0.8. The knee at the same metallicity is observed for [O/Fe], and the MP plateau is formed at [O/Fe]=0.61. (ii) The upward trend of [C/O] with decreasing metallicity exists at [Fe/H]<-1.2, supporting the earlier finding of Akerman et al. (iii) An underabundance of Na relative to Mg in the [Fe/H]<-1 stars is nearly constant, with the mean [Na/Mg]~-0.5. (iv) The K/Sc, Ca/Sc, and Ti/Sc ratios form well-defined trends, suggesting a common site of the K-Ti production. (v) Sr follows the Fe abundance down to [Fe/H]~-2.5, while Zr is enhanced in MP stars. (vi) The comparisons of our results with some widely used Galactic evolution models are given. The use of the NLTE element abundances gives increased credit to the interpretation of the data in the context of the chemical evolution of the Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/687/78
- Title:
- FeII emission in quasars
- Short Name:
- J/ApJ/687/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Broad FeII emission is a prominent feature of the optical and ultraviolet spectra of quasars. We report on a systematical investigation of optical FeII emission in a large sample of 4037 z<0.8 quasars selected from the SDSS-DR5 quasar catalog (Cat. VII/252). We have developed and tested a detailed line-fitting technique, taking into account the complex continuum and narrow and broad emission-line spectra. Our primary goal is to quantify the velocity broadening and velocity shift of the FeII spectrum in order to constrain the location of the FeII-emitting region and its relation to the broad-line region. We find that the majority of quasars show FeII emission that is redshifted, typically by ~400km/s, but up to 2000km/s, with respect to the systemic velocity of the narrow-line region or of the conventional broad-line region as traced by the H{beta} line. Moreover, the line width of FeII is significantly narrower than that of the broad component of H{beta}. We show that the magnitude of the FeII redshift correlates inversely with the Eddington ratio, and that there is a tendency for sources with redshifted FeII emission to show red asymmetry in the H{beta} line. These characteristics strongly suggest that FeII originates from a location different from, and most likely exterior to, the region that produces most of H{beta}. The FeII-emitting zone traces a portion of the broad-line region of intermediate velocities whose dynamics may be dominated by infall.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/86
- Title:
- FeII emission in SDSS type 1 AGNs
- Short Name:
- J/ApJ/736/86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used a large, homogeneous sample of 4178 z<=0.8 Seyfert 1 galaxies and QSOs selected from the Sloan Digital Sky Survey to investigate the strength of FeII emission and its correlation with other emission lines and physical parameters of active galactic nuclei. We find that the strongest correlations of almost all the emission-line intensity ratios and equivalent widths (EWs) are with the Eddington ratio (L/L_Edd_), rather than with the continuum luminosity at 5100{AA} (L_5100_) or black hole mass (M_BH_); the only exception is the EW of ultraviolet FeII emission, which does not correlate at all with broad-line width, L_5100_, M_BH_, or L/L_Edd_. By contrast, the intensity ratios of both the ultraviolet and optical FeII emission to MgII{lambda}2800 correlate quite strongly with L/L_Edd_. Interestingly, among all the emission lines in the near-UV and optical studied in this paper (including MgII{lambda}2800, H{beta}, and [OIII]{lambda}5007), the EW of narrow optical FeII emission has the strongest correlation with L/L_Edd_. We hypothesize that the variation of the emission-line strength in active galaxies is regulated by L/L_Edd_ because it governs the global distribution of the hydrogen column density of the clouds gravitationally bound in the line-emitting region, as well as its overall gas supply. The systematic dependence on L/L_Edd_ must be corrected when using the FeII/MgII intensity ratio as a measure of the Fe/Mg abundance ratio to study the history of chemical evolution in QSO environments.
