Local star-forming galaxies show properties that are thought to differ from galaxies in the early Universe. Among them, the ionizing stellar populations and the gas geometry make the recipes designed to derive chemical abundances from nebular emission lines to differ from those calibrated in the Local Universe. A sample of 1969 Extreme Emission Line Galaxies (EELGs) at a redshift 0 < z < 0.49, selected from the Sloan Digital Sky Survey (SDSS) to be local analogues of high-redshift galaxies, was used to analyze their most prominent emission lines and to derive total oxygen abundances and nitrogen-to-oxygen ratios following the direct method in the ranges 7.7 < 12+log(O/H) < 8.6 and -1.8 < log(N/O) < -0.8. They allow us to obtain new empirically calibrated strong-line methods and to evaluate other recipes based on photoionization models that can be later used for a chemical analysis of actively star-forming galaxies in very early stages of galaxy evolution. Our new relations are in agreement with others found for smaller samples of objects at higher redshifts. When compared with other relations calibrated in the local Universe, they differ when the employed strong-line ratio depends on the hardness of the ionizing radiation, such as O32 or Ne3O2, but they do not when the main dependence is on the ionization parameter, such as S23. In the case of strong-line ratios depending on [NII] lines, the derivation of O/H becomes very uncertain due to the very high N/O values derived in this sample, above all in the low-metallicity regime. Finally, we adapt the bayesian-like code HII-Chi-mistry for the conditions found in this kind of galaxies and we prove that it can be used to derive within errors both O/H and N/O, in consistency with the direct method .
We present the calibration of the [$α/$Fe] element in terms of ultra-violet excess for 465 dwarf stars with spectral type F0-K2. We used a single calibration, fitted to a third degree polynomial with a square of the correlation coefficient 0.74 and standard deviation 0.05 mag, for all stars due to their small colour range, $0.1<(g-r)_0\leq 0.6$ mag, and high frequency in the blueward of the spectrum which minimize the guillotine effect. Our calibration provides [$α/$Fe] elements in the range $(-0.05, 0.35]$ dex. We applied the procedure to a high-latitude field, $85^\circ \leq b \leq 90^\circ$…
We present a semi-empirical calibration between the metallicity ($Z$) of Seyfert 2 Active Galactic Nuclei and the $N2$=log([N II]$λ$6584/H$α$) emission-line intensity ratio. This calibration was derived through the [O III]$λ$5007/[O II]$λ$3727 versus $N2$ diagram containing observational data and photoionization model results obtained with the Cloudy code. The observational sample consists of 463 confirmed Seyfert 2 nuclei (redshift $z < 0.4$) taken from the Sloan Digital Sky Survey DR7 dataset. The obtained $Z$-$N2$ relation is valid for the range $0.3 < (Z/Z_{\odot}) < 2.0$ which corresponds…
Based on SDSS g, r and SCUSS (South Galactic Cap of u-band Sky Survey) $u$ photometry, we develop a photometric calibration for estimating the stellar metallicity from $u-g$ and $g-r$ colors by using the SDSS spectra of 32,542 F- and G-type main sequence stars, which cover almost $3700$ deg$^{2}$ in the south Galactic cap. The rms scatter of the photometric metallicity residuals relative to spectrum-based metallicity is $0.14$ dex when $g-r<0.4$, and $0.16$ dex when $g-r>0.4$. Due to the deeper and more accurate magnitude of SCUSS $u$ band, the estimate can be used up to the faint magnitude of…
We derive new empirical calibrations for strong-line diagnostics of gas phase metallicity in local star forming galaxies by uniformly applying the Te method over the full metallicity range probed by the Sloan Digital Sky Survey (SDSS). To measure electron temperatures at high metallicity, where the auroral lines needed are not detected in single galaxies, we stacked spectra of more than 110,000 galaxies from the SDSS in bins of log[O II]/H$β$ and log[O III]/H$β$. This stacking scheme does not assume any dependence of metallicity on mass or star formation rate, but only that galaxies with the s…
The ionizing source of Low Ionization Nuclear Emission Regions (LINERs) is uncertain. Because of this, an empirical relation to determine the chemical abundances of these objects has not been proposed. In this work, for the first time, we derived two semi-empirical calibrations based on photoionization models to estimate the oxygen abundance of LINERS as a function of the $N2$ and $O3N2$ emission-line intensity ratios. These relations were calibrated using oxygen abundance estimations obtained by comparing the observational emission-line ratios of 43 LINER galaxies (taken from the MaNGA survey…
We used the updated [Fe/H] abundances of 168 F-G type dwarfs and calibrated them to a third order polynomial in terms of reduced ultraviolet excess, $δ_{0.41}$ defined with $ugr$ data in the SDSS. We estimated the $M_g$ absolute magnitudes for the same stars via the re-reduced Hipparcos parallaxes and calibrated the absolute magnitude offsets, $ΔM_g$, relative to the intrinsic sequence of Hyades to a third order polynomial in terms of $δ_{0.41}$. The ranges of the calibrations are $-2<$[Fe/H]$\leq$0.3 dex and $4<M_g\leq6$ mag. The mean of the residuals and the corresponding standard deviation …
We study the direct gas-phase oxygen abundance using the well-detected auroral [OIII]4363 line in the stacked spectra of a sample of local analogs of high-redshift galaxies. These local analogs share the same location as $z\sim2$ star-forming galaxies on the Baldwin-Phillips-Terlevich diagram. This type of analog has the same ionized interstellar medium (ISM) properties as high-redshift galaxies. We establish empirical metallicity calibrations between the direct gas-phase oxygen abundances ($7.8<12+\log(\rm{O/H})<8.4$) and the N2/O3N2 indices in our local analogs. We find significant systemati…
Extremely variable quasars (EVQs) are a population of sources showing large optical photometric variability revealed by time-domain surveys. The physical origin of such extreme variability is yet unclear. In this first paper of a series, we construct the largest-ever sample of 14,012 EVQs using photometric data spanning over $>$ 15 years from SDSS and Pan-STARRS1. We divide them into five sub-samples according to the relative brightness of an EVQ during SDSS spectroscopic observation compared to the mean brightness from photometric observations. Corresponding control samples of normal quasars …
We extend the SDSS Stripe 82 Standard Stars Catalog with post-2007 SDSS imaging data. This improved version lists averaged SDSS ugriz photometry for nearly a million stars brighter than r~22 mag. With 2-3x more measurements per star, random errors are 1.4-1.7x smaller than in the original catalog, and about 3x smaller than for individual SDSS runs. Random errors in the new catalog are ~< 0.01 mag for stars brighter than 20.0, 21.0, 21.0, 20.5, and 19.0 mag in u, g, r, i, and z-bands, respectively. We achieve this error threshold by using the Gaia Early Data Release 3 (EDR3) Gmag photometry to …
In this paper we use strong line calibrations of N/O and O/H in MaNGA spaxel data to explore the systematics introduced by variations in N/O on various strong-line metallicity diagnostics. We find radial variations in N/O at fixed O/H which correlate with total galaxy stellar-mass; and which can induce $\sim 40 \%$ systematic uncertainties in oxygen abundance gradients when nitrogen-dependent abundance calibrations are used. Empirically, we find that these differences are associated with variation in the local star formation efficiency, as predicted by recent chemical evolution models for gala…
We present a cross-calibration of CO- and dust-based molecular gas masses at $z \leqslant 0.2$. Our results are based on a survey with the IRAM 30-m telescope collecting CO(1-0) measurements of 78 massive ($\log M_{\star} / M_{\odot} > 10$) galaxies with known gas-phase metallicities, and with IR photometric coverage from WISE (22 $μ$m ) and Herschel SPIRE (250, 350, 500 $μ$m). We find a tight relation ($\sim 0.17$ dex scatter) between the gas masses inferred from CO and dust continuum emission, with a minor systematic offset of 0.05 dex. The two methods can be brought into agreement by applyi…
With the goal of investigating the degree to which the total infrared luminosity ($L_{\rm TIR}$) traces the star formation rate (SFR), we analyze the $L_{\rm TIR}$ from the dust in a sample of $\sim$ 6000 star-forming galaxies, based on the 3.4, 4.6, 12 and 22 $μ$m data from the Wide-field Infrared Survey Explorer (WISE) and u, g, r, i, z band data from SDSS DR9. These star-forming galaxies are selected by matching the WISE All Sky Catalog with the star-forming galaxy catalog in SDSS DR9 provided by JHU/MPA\thanks{$http://www.sdss3.org/dr9/spectro/spectroaccess.php$}. The values of $L_{\rm TIR…
We present a spectroscopic study of eight extremely low-metallicity candidate emission-line galaxies with oxygen abundances possibly below 12 +log O/H = 7.35. These galaxies were selected from Data Release 10 of the Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey (SDSS/BOSS DR10). We will call these extremely metal-deficient galaxies XMD galaxies. The electron temperature-sensitive emission line [O~{\sc iii}] $λ$4363 is detected in three galaxies and marginally detected in two galaxies, allowing for abundance determination by a "direct" method. Because of large uncertainties i…
SDSS J2232-0806 (the 'Big Dipper') has been identified as a 'slow-blue nuclear hypervariable': a galaxy with no previously known active nucleus, blue colours and large-amplitude brightness evolution occurring on a timescale of years. Subsequent observations have shown that this source does indeed contain an active galactic nucleus (AGN). Our optical photometric and spectroscopic monitoring campaign has recorded one major dimming event (and subsequent rise) over a period of around four years; there is also evidence of previous events consistent with this in archival data recorded over the last …
Motivated by the challenges of calculating the dynamical masses of late-type galaxies (LTGs) and the enormous amount of data from the Sloan Digital Sky Survey (SDSS), we calculate virial masses of a sample of approximately 126,000 LTGs from the sixteenth data release of the SDSS. The virial mass estimations were made considering Newtonian mechanics, virial equilibrium and velocity dispersion from stars and gas. The procedure gave as a result seven mass estimations for each galaxy. The calculated masses were calibrated using a sample of spiral galaxies with velocity rotation curves. Considering…
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), one of three core programs in the Sloan Digital Sky Survey-IV (SDSS-IV), is an integral-field spectroscopic (IFS) survey of roughly 10,000 nearby galaxies. It employs dithered observations using 17 hexagonal bundles of 2 arcsec fibers to obtain resolved spectroscopy over a wide wavelength range of 3,600-10,300A. To map the internal variations within each galaxy, we need to perform accurate {\it spectral surface photometry}, which is to calibrate the specific intensity at every spatial location sampled by each individual aperture elem…
The Mysterious Case of Iron in XMPs: Anomalous High log(Fe/O) Observed in Extremely Metal-Poor Galaxies HSCJ1631+4426 and SDSSJ0811+4730
Swinburne University of Technology（斯威本科技大学）；The University of Sydney（悉尼大学）；University of Queensland（昆士兰大学）；University of Western Australia（西澳大学）；Astronomy Australia Ltd.（澳大利亚天文学有限公司）；The University of Oklahoma（俄克拉荷马大学）
The red giant branch tip in the SDSS, PS1, JWST, NGRST and Euclid photometric systems. Calibration in optical passbands using Gaia DR3 synthetic photometry
We present and discuss the properties of an ionized component with extreme kinematics in an off-nuclear HII region located at 0.8 - 1.0 kpc from the nucleus of SDSS J143245.98+404300.3, recently reported in Rodriguez del Pino et al. (2019). The high-velocity gas component is identified by the detection of very broad emission wings in the Halpha line, with Full Width at Half Maximum (FWHM) > 850-1000 kms-1. Such gas kinematics are outstandingly high compared to other HII regions in local galaxies and similar to those reported in some star-forming clumps of galaxies at redshift around 2. The spa…
We explore indirect methods to detect Polycyclic Aromatic Hydrocarbons (PAHs) in gas-rich, absorption-selected galaxies at high redshift. We look at the optical VLT/X-shooter observations of an intervening, extremely strong damped Lyman-alpha absorber (or ESDLA, with log(N(HI))>~21.7)) towards QSO SDSS J1143+1420 at redshift, z(ESDLA)=2.323. Literature studies have shown that this ESDLA contains signatures of dust and diffuse molecular hydrogen and it was specifically chosen for our study due to its close spatial proximity (impact parameter, rho=0.6+/-0.3 kpc) with its associated galaxy. There…
Using ~1,700,000 target- and sky-fiber spectra from the SDSS, we have carried out a systematic search for Galactic planetary nebulae (PNe) via detections of the [OIII] 4959, 5007 lines. Thanks to the excellent sensitivity of the SDSS spectroscopic surveys, this is by far the deepest search for PNe ever taken, reaching a surface brightness of the [OIII] 5007 line down to about 29.0 mag./arcsec^2. The search recovers 13 previously known PNe in the Galactic Caps. In total, 44 new PN candidates are identified, including 7 candidates of multiple detections and 37 candidates of single detection. The…
We improve the identification and isolation of individual stellar populations in the Galactic halo based on an updated set of empirically calibrated stellar isochrones in the Sloan Digital Sky Survey (SDSS) and Pan-STARRS 1 (PS1) photometric systems. Along the Galactic prime meridian ($l=0^{\circ}$ and $180^{\circ}$), where proper motions and parallaxes from Gaia DR2 can be used to compute rotational velocities of stars in the rest frame of the Milky Way, we use the observed double color-magnitude sequences of stars having large transverse motions, which are attributed to groups of stars in th…
We compare the oxygen abundance (O/H) of the Narrow Line Regions (NLRs) of Seyfert 2 AGNs obtained through strong-line methods and from direct measurements of the electron temperature (Te-method). The aim of this study is to explore the effects of the use of distinct methods on the range of metallicity and on the mass-metallicity relation of AGNs at low redshifts (z < 0.4). We used the Sloan Digital Sky Survey (SDSS) and NASA/IPAC Extragalactic Database (NED) to selected optical (3000 < A < 7000) emission line intensities of 463 confirmed Seyfert 2 AGNs. The oxygen abundance of the NLRs were e…
We present a sample of low-redshift (z<0.133) candidates for extremely low-metallicity star-forming galaxies with oxygen abundances 12+logO/H<7.4 selected from the Data Release 14 (DR14) of the Sloan Digital Sky Survey (SDSS). Three methods are used to derive their oxygen abundances. Among these methods two are based on strong [OII]3727, [OIII]4959, and [OIII]5007 emission lines, which we call strong-line and semi-empirical methods. These were applied for all galaxies. We have developed one of these methods, the strong-line method, in this paper. This method is specifically focused on the accu…
We present the discovery of Balmer line absorption from H$α$ to H$γ$ in an iron low-ionization broad absorption line (FeLoBAL) quasar SDSS J152350.42+391405.2 (hereafter J1523), by the quasi-simultaneous optical and near-infrared spectroscopy. The Balmer line absorption is at $z_{absor}$ = 0.6039 +/-0.0021 and blueshifted by v=10,353 km/s with respect to the Balmer emission lines. All Balmer BALs have uniform absorption profile with the widths of $Δ$ v ~12,000 km/s. We also found the absorption trough in He 1* $λ$10830 with the same velocity and width in the H-band TripleSpec spectrum of J1523…
We present the discovery of an extremely-luminous dust-obscured galaxy (DOG) at $z_{\rm spec}$ = 3.703, WISE J101326.25+611220.1. This DOG is selected as a candidate of extremely-luminous infrared (IR) galaxies based on the photometry from the Sloan Digital Sky Survey and Wide-field Infrared Survey Explorer. In order to derive its accurate IR luminosity, we perform follow-up observations at 450 and 850 $μ$m using the Submillimetre Common User Bolometer Array 2 on the James Clerk Maxwell Telescope, and at 870 and 1300 $μ$m using the Submillimeter Array, which enable us to pin down its IR Spectr…
We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] < -3.0) star, SDSS J134338.67+484426.6, identified during the course of the MARVELS spectroscopic pre-survey of some 20000 stars to identify suitable candidates for exoplanet searches. This star, with an apparent magnitude V = 12.14, is the lowest metallicity star found in the pre-survey, and is one of only ~20 known EMP stars that are this bright or brighter. Our high-resolution spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42, having "normal" carbon and no enhancement of neutron-ca…
Accurately determining the mass of galaxy clusters is fundamental for many studies on cosmology and galaxy evolution. We collect and rescale the cluster masses of 1191 clusters of 0.05<z<0.75 estimated by X-ray or Sunyaev-Zeldovich measurements and use them to calibrate the optical mass proxy. The total r-band luminosity (in units of L^{\ast}) of these clusters are obtained by using spectroscopic and photometric data of the Sloan Digital Sky Survey (SDSS). We find that the correlation between the cluster mass M_{500} and total r-band luminosity L_{500} significantly evolves with redshift. Afte…
We report extremely faint 144 MHz radio emission from two gravitationally lensed quasars, SDSS J1004+4112 (z = 1.730) and SDSS J2222+2745 (z = 2.803), using the LOFAR Two Metre Sky Survey (LoTSS) data release 2. After correcting for the lensing magnifications, the two objects have intrinsic flux-densities of 13+/-2 and 58+/-6 uJy, respectively, corresponding to 144 MHz rest-frame luminosities of 10^(23.2+/-0.2) and 10^(24.42+/-0.05) W / Hz, respectively. In the case of SDSS J1004+4112, the intrinsic flux density is close to the confusion limit of LoTSS, making this radio source the faintest to…
We report the discovery of extreme X-ray variability in a type 1 quasar: SDSS J$075101.42+291419.1$. It has a black hole mass of $1.6\times 10^7~\rm M_\odot$ measured from reverberation mapping (RM), and the black hole is accreting with a super-Eddington accretion rate. Its XMM-Newton observation in 2015 May reveals a flux drop by a factor of $\sim 22$ with respect to the Swift observation in 2013 May when it showed a typical level of X-ray emission relative to its UV/optical emission. The lack of correlated UV variability results in a steep X-ray-to-optical power-law slope ($α_{\rm OX}$) of -…
We report the discovery of one extremely metal-poor (EMP; [Fe/H]<-3) and one ultra metal-poor (UMP; [Fe/H]<-4) star selected from the SDSS/SEGUE survey. These stars were identified as EMP candidates based on their medium-resolution (R~2,000) spectra, and were followed-up with high-resolution (R~35,000) spectroscopy with the Magellan-Clay Telescope. Their derived chemical abundances exhibit good agreement with those of stars with similar metallicities. We also provide new insights on the formation of the UMP stars, based on comparison with a new set of theoretical models of supernovae nucleosyn…
We present new observations of sixteen bright ($r=19-21$) gravitationally lensed galaxies at $z\simeq 1-3$ selected from the CASSOWARY survey. Included in our sample is the $z=1.42$ galaxy CSWA-141, one of the brightest known reionization-era analogs at high redshift (g=20.5), with a large sSFR (31.2 Gyr$^{-1}$) and an [OIII]+H$β$ equivalent width (EW$_{\rm{[OIII]+Hβ}}$=730~Å) that is nearly identical to the average value expected at $z\simeq 7-8$. In this paper, we investigate the rest-frame UV nebular line emission in our sample with the goal of understanding the factors that regulate strong…
We introduce the ongoing MaStar project, which is going to construct a large, well-calibrated, high quality empirical stellar library with more than 8000 stars covering the wavelength range from 3622 to 10,354A at a resolution of R~2000, and with better than 3% relative flux calibration. The spectra are taken using hexagonal fiber bundles feeding the BOSS spectrographs on the 2.5m Sloan Foundation Telescope, by piggybacking on the SDSS-IV/APOGEE-2 observations. Compared to previous efforts of empirical libraries, the MaStar Library will have a more comprehensive stellar parameter coverage, esp…
We report the discovery of an extreme X-ray flux rise (by a factor of > 20) of the weak-line quasar SDSS J153913.47+395423.4 (hereafter SDSS J1539+3954) at z = 1.935. SDSS J1539+3954 is the most-luminous object among radio-quiet type 1 AGNs where such dramatic X-ray variability has been observed. Before the X-ray flux rise, SDSS J1539+3954 appeared X-ray weak compared with the expectation from its UV flux; after the rise, the ratio of its X-ray flux and UV flux is consistent with the majority of the AGN population. We also present a contemporaneous HET spectrum of SDSS J1539+3954, which demons…
Chemical abundance determinations in Low-Ionization Nuclear Line Regions (LINERs) are especially complex and uncertain because the nature of the ionizing source of this kind of object is unknown. In this work, we study the oxygen abundance in relation to the hydrogen abundance (O/H) of the gas phase of the UGC4805 LINER nucleus. Optical spectroscopic data from the Mapping Nearby Galaxies (MaNGA) survey was employed to derive the O/H abundance of the UGC4805 nucleus based on the extrapolation of the disk abundance gradient, on calibrations between O/H abundance and strong emission-lines for Act…
We present the results of an analysis for 107 extremely metal-poor (EMP) stars with metallicities less than [Fe/H] = -3.0, identified from medium-resolution spectra in SDSS. We follow a methodology based on comparisons of the observed spectra with synthetic spectra. The abundances of Fe, Ca, and Mg are determined by fitting spectral regions dominated by lines of each element. In addition, we present a technique to determine upper limits for elements whose features are not detected in a given spectrum. We also analyse our sample with the SEGUE Stellar Parameter Pipeline, in order to obtain addi…
Context. The first generation of stars formed in the Galaxy left behind the chemical signatures of their nucleosynthesis in the interstellar medium, visible today in the atmospheres of low-mass stars formed afterwards. Sampling the chemistry of low-mass provides insight into the first stars. Aims. We aim to increase the samples of stars with extremely low metal abundances, identifying ultra metal-poor stars from spectra with modest spectral resolution and signal-to-noise ratio (S/N). Achieving this goal involves deriving reliable metallicities and carbon abundances from such spectra. Methods. …
For the extremely bright lensed galaxy SDSS J1723+3411 at z=1.3293 , we analyze spatially integrated MMT, Keck, and Hubble Space Telescope spectra that fully cover the rest-frame wavelength range of 1400 to 7200 Angstroms. We also analyze near-IR spectra from Gemini that cover H alpha for a portion of the lensed arc. We report fluxes for 42 detected emission lines, and upper limits for an additional 22. This galaxy has extreme emission line ratios and high equivalent widths that are characteristic of extreme emission-line galaxies. We compute strong emission line diagnostics from both the rest…
We present elemental abundances for eight unevolved extremely metal-poor stars with $T_{\rm eff}>5500\,\mathrm{K}$, among which seven have $[\mathrm{Fe/H}]<-3.5$. The sample is selected from the Sloan Digital Sky Survey / Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE), and our previous high-resolution spectroscopic follow-up with the Subaru Telescope (Aoki et al.). Several methods to derive stellar parameters are compared, and no significant offset in the derived parameters is found in most cases. From an abundance analysis relative to the standard extremely metal-poor…
How can we discover objects we did not know existed within the large datasets that now abound in astronomy? We present an outlier detection algorithm that we developed, based on an unsupervised Random Forest. We test the algorithm on more than two million galaxy spectra from the Sloan Digital Sky Survey and examine the 400 galaxies with the highest outlier score. We find objects which have extreme emission line ratios and abnormally strong absorption lines, objects with unusual continua, including extremely reddened galaxies. We find galaxy-galaxy gravitational lenses, double-peaked emission l…
Extreme coronal-line emitter (ECLE) SDSSJ095209.56+214313.3, known by its strong, fading, high ionization lines, has been a long standing candidate for a tidal disruption event, however a supernova origin has not yet been ruled out. Here we add several new pieces of information to the puzzle of the nature of the transient that powered its variable coronal lines: 1) an optical light curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that serendipitously catches the optical flare, and 2) late-time observations of the host galaxy with the Swift Ultraviolet and Optical Telescope (…
Quasars with extremely red infrared-to-optical colours are an interesting population that can test ideas about quasar evolution as well as orientation, obscuration and geometric effects in the so-called AGN unified model. To identify such a population we match the quasar catalogues of the Sloan Digital Sky Survey (SDSS), the Baryon Oscillation Spectroscopic Survey (BOSS) to the Wide-Field Infrared Survey Explorer (WISE) to identify quasars with extremely high infrared-to-optical ratios. We identify 65 objects with r(AB)-W4(Vega)>14 mag (i.e., F_nu(22um)/F_nu(r) > ~1000). This sample spans a re…
The most metal-poor stars in the Milky Way witnessed the early phases of formation of the Galaxy, and have chemical compositions that are close to the pristine mixture from Big Bang nucleosynthesis, polluted by one or few supernovae. Only two dozen stars with ([Fe/H]< -4) are known, and they show a wide range of abundance patterns. It is therefore important to enlarge this sample. We present the first results of an effort to identify new extremely metal-poor stars in the Milky Way halo. Our targets have been selected from low-resolution spectra obtained as part of the Sloan Digital Sky Survey,…
Recalibration of SDSS photometric zero-points based on the InfraRed Flux Method temperature scale
Yunnan Astronomical Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天体物理与天文研究学院）；International Centre of Supernovae, Yunnan Key Laboratory（超新星国际中心，云南省重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）；Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences（中国科学院天体结构与演化重点实验室）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）
Empirical colour--effective temperature relations in the SDSS system from IRFM temperatures of GALAH and APOGEE stars
Yunnan Astronomical Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天体物理与天文研究学院）；International Centre of Supernovae (ICESUN)（超新星国际中心）；University of the Chinese Academy of Sciences（中国科学院大学）；CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台光学天文重点实验室）
The most metal-poor stars are the relics of the early chemical evolution of the Galaxy. Their chemical composition is an important tool to constrain the nucleosynthesis in the first generation of stars. The aim is to observe a sample of extremely metal-poor star (EMP stars) candidates selected from the Sloan Digital Sky Survey Data Release 12 (SDSS DR12) and determine their chemical composition. We obtain medium resolution spectra of a sample of six stars using the X-Shooter spectrograph at the Very Large Telescope (VLT) and we used ATLAS models to compute the abundances. Five stars of the sam…
