- ID:
- ivo://CDS.VizieR/J/ApJ/877/104
- Title:
- High-res. spectroscopy of LAMOST Li-rich giants
- Short Name:
- J/ApJ/877/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of Li-rich giants has introduced a new challenge for standard stellar evolution models. To resolve this issue, the number of this type of object has been rapidly increased through the development of worldwide surveys. Taking advantage of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, 44 new Li-rich giants are reported, which are confirmed with high-resolution observations. Based on the high-resolution and high signal-to-noise spectra, we derived the atmospheric parameters and elemental abundances with the spectral synthesis method. We performed a detailed analysis of their evolutionary stages, infrared excess, projected rotational velocity (vsini), and stellar population. We find that (1) the Li-rich giants concentrate at the evolutionary status of the red giant branch bump, red clump, and asymptotic giant branch; (2) three of them are fast rotators and none exhibit infrared excess. Our results imply that the origins of Li enrichment are most likely to be associated with the extra mixing in the stellar interior, and the external sources might only make a minor contribution. Moreover, various Li-rich episodes take place at different evolutionary stages.
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- ID:
- ivo://CDS.VizieR/J/ApJ/727/73
- Title:
- High S/N composite spectrum of GRB afterglows
- Short Name:
- J/ApJ/727/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a composite spectrum of 60 long duration gamma-ray burst (GRB) afterglows with redshifts in the range 0.35<z<6.7 observed with low-resolution optical spectra. The composite spectrum covers the wavelength range 700-6600{AA} in the rest frame and has a mean signal-to-noise ratio of 150 per 1{AA} pixel and reaches a maximum of ~300 in the range 2500-3500{AA}. Equivalent widths are measured from metal absorption lines from the Ly{alpha} line to ~5200{AA}, and associated metal and hydrogen lines are identified between the Lyman break and Ly{alpha} line. The average transmission within the Lyman forest is consistent with that found along quasar lines of sight.
- ID:
- ivo://CDS.VizieR/J/AJ/103/514
- Title:
- High-velocity stars toward South Galactic Cap
- Short Name:
- J/AJ/103/514
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectroscopic observations of stars identified in Murray's (1986) astrometric survey of the South Galactic Cap
- ID:
- ivo://CDS.VizieR/J/A+A/652/A23
- Title:
- HII-chi-mistry-IR. Abundances
- Short Name:
- J/A+A/652/A23
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We provide a new method to derive heavy element abundances based on the unique suite of nebular lines in the mid- to far-infrared (IR) range. Using grids of photo-ionisation models that cover a wide range in O/H and N/O abundances, and ionisation parameter, our code HII-CHI-MISTRY-IR (HCm-IR) provides model-based abundances based on extinction free and temperature insensitive tracers, two significant advantages over optical diagnostics. The code is probed using a sample of 56 galaxies observed with Spitzer and Herschel covering a wide range in metallicity, 7.2~<12+log(O/H)~<8.9. The IR model-based metallicities obtained are robust within a scatter of 0.03dex when the hydrogen recombination lines, which are typically faint transitions in the IR range, are not available. When compared to the optical abundances obtained with the direct method,model- based methods, and strong-line calibrations, HCm-IR estimates show a typical dispersion of ~0.2dex, in line with previous studies comparing IR and optical abundances, a do not introduce a noticeable systematic above 12+log(O/H)>7.6. This accuracy can be achieved using the lines [SIV]10.5um, [SIII]18.7,33.5um, [NeIII]15.6um and [NeII]12.8um. Additionally, HCm-IR provides an independent N/O measurement when the [OIII]52,88um and [NIII]57um transitions are measured, and therefore the derived abundances in this case do not rely on particular assumptions in the N/O ratio. Large uncertainties (~0.4dex) may affect the abundance determinations of galaxies at sub- or over-solar metallicities when a solar-like N/O ratio is adopted. Finally, the code has been applied to 8 galaxies located at 1.8<z<7.5 with ground-based detections of far-IR lines redshifted in the submm range, revealing solar-like N/O and O/H abundances in agreement with recent studies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/757
- Title:
- HII complexes optical and IR emissions
- Short Name:
- J/MNRAS/444/757
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of optical spectroscopy and infrared aperture photometry of more than 100 HII complexes in nine galaxies. Spectra obtained with the 6-m telescope of Special Astrophysical Observatory of the Russian Academy of Sciences are used along with archival data from Spitzer and several ground-based telescopes to infer a strength of polycyclic aromatic hydrocarbon (PAH) emission, age, properties of the UV radiation field, and metallicity of studied HII complexes. Physical properties (age, radiation field parameters, metallicity) are related to the F_8_/F_24_ ratio used as a proxy for the PAH abundance in order to reveal factors that may influence the PAH evolution in HII complexes. The well-known correlation between the F_8_/F_24_ ratio and metallicity is confirmed in the studied complexes. The infrared flux ratio also correlates with the [Oiii]{lambda}5007/H{beta} ratio which is often considered as an indicator of the radiation field hardness, but this correlation seems to be a mere reflection of a correlation between [Oiii]{lambda}5007/H{beta} and metallicity. In separate metallicity bins, the F_8_/F_24_ ratio is found to correlate with an age of an Hii complex, which is estimated from the equivalent width of H{beta} line. The correlation is positive for low-metallicity complexes and negative for high-metallicity complexes. Analysing various mechanisms of PAH formation and destruction in the context of found correlations, we suggest that PAH abundance is likely altered by the UV radiation within HII complexes, but this is not necessarily due to their destruction. If PAHs can also form in Hii complexes due to some processes like aromatization, photodestruction, shattering and sputtering of very small grains, the net F_8_/F_24_ ratio is determined by a balance between all these processes that can be different at different metallicities.
- ID:
- ivo://CDS.VizieR/J/ApJ/830/4
- Title:
- HII region abundances in NGC 5457 (M101)
- Short Name:
- J/ApJ/830/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Large Binocular Telescope observations of 109 HII regions in NGC 5457 (M101) obtained with the Multi-Object Double Spectrograph. We have robust measurements of one or more temperature-sensitive auroral emission lines for 74 HII regions, permitting the measurement of "direct" gas-phase abundances. Comparing the temperatures derived from the different ionic species, we find: (1) strong correlations of T[NII] with T[SIII] and T[OIII], consistent with little or no intrinsic scatter; (2) a correlation of T[SIII] with T[OIII], but with significant intrinsic dispersion; (3) overall agreement between T[NII], T[SII], and T[OII], as expected, but with significant outliers; (4) the correlations of T[NII] with T[SIII] and T[OIII] match the predictions of photoionization modeling while the correlation of T[SIII] with T[OIII] is offset from the prediction of photoionization modeling. Based on these observations, which include significantly more observations of lower excitation HII regions, missing in many analyses, we inspect the commonly used ionization correction factors (ICFs) for unobserved ionic species and propose new empirical ICFs for S and Ar. We have discovered an unexpected population of HII regions with a significant offset to low values in Ne/O, which defies explanation. We derive radial gradients in O/H and N/O which agree with previous studies. Our large observational database allows us to examine the dispersion in abundances, and we find intrinsic dispersions of 0.074+/-0.009 in O/H and 0.095+/-0.009 in N/O (at a given radius). We stress that this measurement of the intrinsic dispersion comes exclusively from direct abundance measurements of HII regions in NGC 5457.
- ID:
- ivo://CDS.VizieR/J/ApJ/602/200
- Title:
- HII regions abundances in blue compact galaxies
- Short Name:
- J/ApJ/602/200
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use spectroscopic observations of a sample of 82 HII regions in 76 blue compact galaxies to determine the primordial helium abundance Yp and the slope dY/dZ from the Y-O/H linear regression. To improve the accuracy of the dY/dZ measurement, we have included new spectrophotometric observations of 33 HII regions that span a large metallicity range, with oxygen abundance 12+log(O/H) varying between 7.43 and 8.30 (Z_{sun}_/30<=Z<=Z_{sun}_/4). Most of the new galaxies were selected from the First Byurakan, the Hamburg/SAO, and the University of Michigan objective prism surveys.
- ID:
- ivo://CDS.VizieR/J/ApJ/655/814
- Title:
- HII regions in IC 342/Maffei group
- Short Name:
- J/ApJ/655/814
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained spectra of HII regions in the heavily obscured spiral galaxy Maffei 2. The observations have allowed for a determination of the Galactic extinction of this galaxy using a correlation between extinction and hydrogen column density observed among spiral galaxies.
- ID:
- ivo://CDS.VizieR/J/other/RAA/14.1393
- Title:
- HII regions in interacting system Arp 86
- Short Name:
- J/other/RAA/14.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the metallicity and star formation activities of HII regions in the interacting system Arp 86, based on the first scientific observations using multi-object spectroscopy with the 2.16m telescope at the Xinglong Observing Station. We find that the oxygen abundance gradient in Arp 86 is flatter than that in normal disk galaxies, which confirms that gas inflows caused by tidal forces during encounters can flatten the metallicity distributions in galaxies. The companion galaxy NGC 7752 is currently experiencing a galaxy-wide starburst with a higher star formation rate surface density than the main galaxy NGC 7753, which can be explained in that the companion galaxy is more susceptible to the effects of interaction than the primary. We also find that the galaxy 2MASX J23470758+2926531 has similar abundance and star formation properties to NGC 7753, and may be a part of the Arp 86 system.
- ID:
- ivo://CDS.VizieR/J/A+A/529/A149
- Title:
- HII regions in low-metallicity galaxies
- Short Name:
- J/A+A/529/A149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep spectroscopy of a large sample of low-metallicity emission-line galaxies. The main goal of this study is to derive element abundances in these low-metallicity galaxies. We analyze 121 VLT spectra of HII regions in 46 low-metallicity emission-line galaxies. Of these spectra 83 are archival VLT/FORS1+UVES spectra of HII regions in 31 low-metallicity emission-line galaxies that are studied for the first time with standard direct methods to determine the electron temperatures, the electron number densities, and the chemical abundances.
