- ID:
- ivo://CDS.VizieR/J/A+A/643/A80
- Title:
- sample of HeII-emitters abundances
- Short Name:
- J/A+A/643/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star-forming galaxies with nebular HeII emission contain very energetic ionizing sources of radiation, which can be considered as analogs to the major contributors of the reionization of the Universe in early epochs. It is therefore of great importance to provide a reliable absolute scale for the equivalent effective temperature (T*) for these sources. We study a sample of local (z<0.2) star-forming galaxies showing optical nebular HeII emission using the so-called softness diagrams, involving emission lines of two elements in two consecutive stages of ionization (e.g., [SII]/[SIII] vs. [OII]/[OIII]). We use for the first time the HeI/HeII ratio in these diagrams in order to explore the higher range of T* expected in these objects, and to investigate the role of possible mechanisms driving the distribution of galaxy points in these diagrams. We build grids of photoionization models covering different black-body temperatures, model cluster atmospheres, and density-bounded geometries to explain the conditions observed in the sample. We verified that the use of the softness diagrams including the emission-line ratio HeI/HeII combined with black-body photoionization models can provide an absolute scale of T* for these objects. The application of a Bayesian-like code indicates T* in the range 50-80kK for the sample of galaxies, with a mean value higher than 60kK. The average of these high temperature values can only be reproduced using cluster model populations with nearly metal-free stars, although such ionizing sources cannot explain either the highest T* values, beyond 1{sigma}, or the dispersion observed in the softness diagrams. According to our photoionization models, most sample galaxies could be affected to some extent by ionizing photon leaking, presenting a mean photon absorption fraction of 26% or higher depending on the metallicity assumed for the ionizing cluster. The entire range of HeI/HeII, [SII]/[SIII], and [OII]/[OIII] ratios for these HeII-emitting galaxies is reproduced with our models, combining nearly metal-free ionizing clusters and photon leaking under different density-bounded conditions.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/623/A122
- Title:
- Sample of MaNGA galaxies properties
- Short Name:
- J/A+A/623/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive rotation curves, surface brightness profiles, and oxygen abundance distributions for 147 late-type galaxies using the publicly available spectroscopy obtained by the MaNGA survey. Changes of the central oxygen abundance (O/H)_0_, the abundance at the optical radius (O/H)_R25_, and the abundance gradient with rotation velocity V_rot_ were examined for galaxies with rotation velocities from 90km/s to 350km/s. We find that each relation shows a break at V_rot_^*^~200km/s. The central (O/H)_0_ abundance increases with rising V_rot_ and the slope of the (O/H)_0_-V_rot_ relation is steeper for galaxies with V_rot_<=V_rot_^*^. The mean scatter of the central abundances around this relation is 0.053 dex. The relation between the abundance at the optical radius of a galaxy and its rotation velocity is similar; the mean scatter in abundances around this relation is 0.081 dex. The radial abundance gradient expressed in dex/kpc flattens with the increase of the rotation velocity. The slope of the relation is very low for galaxies with V_rot_>=V_rot_^*^. The abundance gradient expressed in dex/R_25_ is roughly constant for galaxies with V_rot_<=V_rot_^*^, flattens towards V_rot_^*^, and then again is roughly constant for galaxies with V_rot_>=V_rot_^*^. The change of the gradient expressed in terms of dex/h_d_ (where h_d_ is the disc scale length), in terms of dex/R_e,d_ (where R_e,d_ is the disc effective radius), and in terms of dex/R_e,g_ (where R_e,g_ is the galaxy effective radius) with rotation velocity is similar to that for gradient in dex/R_25_. The relations between abundance characteristics and other basic parameters (stellar mass, luminosity, and radius) are also considered.
- ID:
- ivo://CDS.VizieR/J/A+A/508/355
- Title:
- Scaled solar tracks and isochrones
- Short Name:
- J/A+A/508/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We extend our theoretical computations for low-mass stars to intermediate-mass and massive stars, for which few databases exist in the literature. Evolutionary tracks and isochrones are computed for initial masses 2.50-20M_{sun}_ for a grid of 37 chemical compositions with metal content Z between 0.0001 and 0.070 and helium content Y between 0.23 and 0.40 to enable users to obtain isochrones for ages as young as about 10^7^ years and to simulate stellar populations with different helium-to-metal enrichment laws. The Padova stellar evolution code is identical to that used in the first paper of this series. Synthetic TP-AGB models allow stellar tracks and isochrones to be extended until the end of the thermal pulses along the AGB. We provide software tools for the bidimensional interpolation (in Y and Z) of the isochrones from very old ages down to about 10^7^ years. This lower limit depends on chemical composition. The extension of the blue loops and the instability strip of Cepheid stars are compared and the Cepheid mass-discrepancy is discussed. The location of red supergiants in the H-R diagram is in good agreement with the evolutionary tracks for masses from 10 to 20M_{sun}_. Tracks and isochrones are available in tabular form for the adopted grid of chemical compositions in the extended plane Z-Y in three photometric systems. An interactive web interface allows users to obtain isochrones of any chemical composition inside the provided Z-Y range and also to simulate stellar populations with different Y(Z) helium-to-metal enrichment laws.
- ID:
- ivo://CDS.VizieR/II/47
- Title:
- Scanner Abundance in late-type evolved stars
- Short Name:
- II/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Abundance parameters have been derived from scanner observations of 229 stars. Observations were made with the Wampler photoelectric spectrum scanner (Wampler, 1966) on Lick Observatory's Crossley and 120inch telescopes. Data reductions were performed at UC Berkeley on the IBM 7094 computer using programs by L.V. Kuhi and B.J. Taylor. The method of reduction and the photometric standard system are described by Spinrad and Taylor (1969AJ.....72..320S). The file "color.dat" (tables 5 and 6 in the publication) gives colors between 3880 and 7400{AA} for program stars and survey stars, normalized so that I(5360)=1000. The file "block.dat" gives the blocking fractions for program stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/363/734
- Title:
- Sculptor dSph variables metal abundances
- Short Name:
- J/MNRAS/363/734
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-resolution spectroscopy obtained with FORS2 at the Very Large Telescope (VLT) has been used for the measurement of individual metal abundances ([Fe/H]) for 110 variable stars, including 107 RR Lyrae stars and one anomalous Cepheid, and to trace the metal distribution of the oldest stellar component in the Sculptor dwarf spheroidal galaxy. The RR Lyrae stars are spread over a 15x15arcmin^2^ area around the galaxy centre.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A15
- Title:
- Sculptor Red Giant Branch stars abundances
- Short Name:
- J/A+A/626/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed chemical abundances for 99 Red Giant Branch stars in the centre of the Sculptor dwarf spheroidal galaxy, which have been obtained from high-resolution VLT/FLAMES spectroscopy. The abundances of Li, Na, alpha-elements (O, Mg, Si, Ca Ti), iron-peak elements (Sc, Cr, Fe, Co, Ni, Zn), r- and s-process elements (Ba, La, Nd, Eu) were all derived using stellar atmosphere models and semi-automated analysis techniques. The iron abundances, covering the range -2.3<[Fe/H]<-0.9, populate the whole metallicity distribution of the galaxy with the exception of the very low metallicity tail. There is a marked decrease in [{alpha}/Fe] over our sample, from the Galactic halo plateau value at low [Fe/H] and then, after a 'knee', a decrease to sub-solar [alpha/Fe] at high [Fe/H]. This is consistent with products of core-collapse supernovae dominating at early times, followed by the onset of supernovae type Ia as early as ~12Gyr ago. The products from low-mass AGB stars, as traced by the s-process, also participate in the chemical evolution of Sculptor with a timescale comparable to that of supernovae type Ia. However, the r-process is consistent with having no time delay relative to core-collapse supernovae, at least at the later stages of the chemical evolution in Sculptor. Using the simple and well-behaved chemical evolution of Sculptor, we further derive empirical constraints on the relative importance of massive stars and supernovae type Ia to the nucleosynthesis of individual iron-peak and alpha-elements. The most important contribution of supernovae typeIa is to the iron-peak elements: Fe, Cr and Mn; but there is also a modest but non-negligible contribution to both the heavier alpha-elements: S, Ca and Ti, and some of the iron-peak elements: Sc and Co. We see only very small or no contribution to O, Mg, Ni and Zn from supernovae type Ia in Sculptor. The observed chemical abundances in Sculptor show no evidence of a significantly different initial mass function, compared to that of the Milky Way. With the exception of neutron-capture elements at low [Fe/H], the scatter around mean trends in Sculptor for [Fe/H]>-2.3 is extremely low, and compatible with observational errors. Combined with the small scatter in the age-elemental abundances relation, this calls for an efficient mixing of metals in the gas in the centre of Sculptor since ~12Gyr ago.
- ID:
- ivo://CDS.VizieR/J/A+A/577/A9
- Title:
- Sc, V, Mn, and Co in Milky Way stars
- Short Name:
- J/A+A/577/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the elemental abundances of a large sample of F and G dwarfs in the solar neighborhood. The analysis is based on high-resolution spectra obtained with MIKE on the Magellan telescope, FEROS on the ESO 1.5m and 2.2m telescopes, HARPS on the ESO 3.6m telescope, UVES on the ESO Very Large Telescope, SOFIN and FIES on the Nordic Optical Telescope. We focused our study on odd-Z iron-peak elements Sc, V, Mn and Co. Our results show that Sc, V, and Co present similar trend as the alpha elements and in Co case, this is true also when non-local thermodynamic equilibrium corrections (non-LTE, NLTE) are applied. On the contrary Mn is generally underabundant relative the Sun but when NLTE corrections are applied the trend is basically flat with [Mn/Fe]=0. Considering the age as selection criterion for thin and thick disk we did not find any difference for V, Co, and Mn LTE while for Sc and Mn NLTE a small difference seem to be present. Comparisons with the alpha-element Ti show flat trends for all the elements except Mn that present well separated [Mn/Ti]-[Ti/H] for thin and thick disk.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/122
- Title:
- SDSS-DR14 and LAMOST DR6 spectra in GD-1 stream
- Short Name:
- J/ApJ/869/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Combining data from Gaia DR2, SDSS DR14, and LAMOST DR6, we update the fit to model of the properties of the stellar stream GD-1 and find that it has an age of ~13Gyr, [Fe/H] of -2.2+/-0.12, and a distance from the Sun of ~8kpc. We tabulate six-dimensional (6D) phase-space fiducial points along the GD-1 stream orbit over a 90{deg} arc. The fitted orbit shows that the stream has an eccentricity e~0.3, perigalacticon of 14.2kpc, apogalacticon of 27.0kpc, and inclination i~40{deg}. There is evidence along the arc for four candidate stellar overdensities, one candidate gap, two candidate stellar underdensities, and that the stream is cut off at {phi}_1_~2{deg} (in the stream-aligned ({phi}_1_, {phi}_2_) coordinate system of Koposov+ 2010ApJ...712..260K). The spur originating at {phi}_1_~-40{deg} implies stars were pulled away from the stream trace by an encounter (potentially a dark matter subhalo). The narrowest place (FWHM~44.6pc) of the GD-1 trace is at ({phi}_1_, {phi}2^c^)~(-14{deg}, 0.15{deg}), which is ~(178.18{deg}, 52.19{deg}) in (RA, DE), where the progenitor is possibly located. We also find six blue horizontal branch and 10 blue stragglers spectroscopic stars in the GD-1 stream.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/130
- Title:
- SDSS-DR7 red HB stars spectroscopic data
- Short Name:
- J/ApJ/751/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have selected 556 red horizontal branch stars along the streams of the Sagittarius (Sgr) dwarf galaxy from Sloan Digital Sky Survey DR7 spectroscopic data using a theoretical model. The metallicity and {alpha}-element distributions are investigated for stars in the Sgr streams and for Galactic stars at the same locations. We find that the Sgr stars have two peaks in the metallicity distribution while the Galactic stars have a more prominent metal-poor peak. Meanwhile, [{alpha}/Fe] ratios of the Sgr stars are lower than those of the Galactic stars. Among the Sgr stars, we find a difference in the metallicity distribution between the leading and trailing arms of the Sgr tidal tails. The metallicity and [{alpha}/Fe] distribution of the leading arm is similar to that of the Galaxy. The trailing arm is composed mainly of a metal-rich component and [{alpha}/Fe] is obviously lower than that of the Galactic stars. The metallicity gradient is -(1.8+/-0.3)x10^-3^dex/deg in the first wrap of the trailing arm and -(1.5+/-0.4)x10^-3^dex/deg in the first wrap of the leading arm. No significant gradient exists along the second wraps of the leading or trailing arms. It seems that the Sgr dwarf galaxy initially lost the metal-poor component in the second wrap (older) arms due to the tidal force of our Galaxy and then the metal-rich component is disrupted in the first wrap (younger) arms. Finally, we found that the velocity dispersion of the trailing arm from 88{deg}<{Lambda}_{sun}_<112{deg} is {sigma}=9.808+/-1.0km/s, which is consistent with previous work in the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/546/A122
- Title:
- SDSS extremely metal-poor emission-line galaxies
- Short Name:
- J/A+A/546/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 6.5-m MMT and 3.5m APO spectrophotometry of 69 HII regions in 42 low-metallicity emission-line galaxies, selected from the data release 7 of the Sloan Digital Sky Survey to have mostly [OIII]{lambda}4959/H{beta}<~1 and [NII]{lambda}6583/H{beta}<~0.1. The electron temperature-sensitive emission line [OIII]{lambda}4363 is detected in 53 HII regions allowing a direct abundance determination. The oxygen abundance in the remaining 16 HII regions is derived using a semi-empirical method. The oxygen abundance of the galaxies in our sample ranges from 12+logO/H~7.1 to ~7.9, with 14 HII regions in 7 galaxies with 12+logO/H<=7.35. In 5 of the latter galaxies, the oxygen abundance is derived here for the first time. Including other known extremely metal-deficient emission-line galaxies from the literature, e.g. SBS 0335-052W, SBS 0335-052E and I Zw 18, we have compiled a sample of the 17 most metal-deficient (with 12+logO/H<=7.35) emission-line galaxies known in the local universe. There appears to be a metallicity floor at 12+log O/H~6.9, suggesting that the matter from which dwarf emission-line galaxies formed was pre-enriched to that level by e.g. Population III stars.
