J/A+A/707/A308ivo://CDS.VizieR/J/A+A/707/A308CDSMontelius M.Angrilli Muglia A.Starkenburg E.Kobayashi C.,Ardern-Arentsen A.Gran F.Jablonka P.Martin N.Navarro J.Sestito F.,Venn K.A.Vitali S.2026-03-19T07:07:15Z2026-03-19T08:06:36ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frmilky-way-galaxymagellanic-cloudsinfrared-astronomyspectroscopychemically-peculiar-starsVery metal-poor stars are important tracers of the early chemical evolution history of the Milky Way. Infrared H-band spectroscopic surveys, such as APOGEE, are less affected by extinction in the more dust-obscured environments of our Galaxy. However, H-band spectra contain very limited spectral information for stars at the most metal-poor tail ([Fe/H]<-2.5) due to the weakness of available Fe lines in FGK stars in this wavelength range. The first paper in this series successfully identified a sample of 327 very metal-poor stars (with [Fe/H]<-2) from the APOGEE database, out of which 289 stars are on the red giant branch. These spectra were not properly analysed by the APOGEE main pipeline due to their very metal-poor nature. In this work, we measure metallicities for these stars, using the abundances of the elements Mg and Si. We demonstrate that the elements Mg and Si have good quality absorption lines despite the challenging combination of (low) metallicity, wavelength regime, spectral resolution, and signal-to-noise ratios available for these spectra. A specialized pipeline is designed to measure the abundance of Mg and Si in APOGEE spectra, which yields a robust estimate of the overall metallicity. In order to provide reliable measurements, we test 3 different sets of assumptions for Mg and Si enhancement. We present Mg and Si abundances as well as overall metallicities for 327 stars, all of which had previously gotten null values from the main APOGEE pipeline for either the calibrated [M/H] or [Fe/H]. Typical uncertainties for our measurements are 0.2dex. We find in our sample 5 stars with unusually high Si/Mg abundances above 0.5, a signature we connect to globular cluster stars, and that might be related to specific supernova events. Our data suggest a concentration of high Si/Mg stars in the Sextans dwarf galaxy. Other dwarf galaxies are found to be in good agreement with results found in the literature. Our derived metallicities range between -3.1<=[M/H]<=-2.25, thereby pushing the metal-poor tail of APOGEE results down by 0.6dex.2026A&A...707A.308Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/707/A308CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)III/286 : APOGEE-2 DR17 final allStar catalog (Abdurro'uf+, 2022)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/707/A308https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/707/A308http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/707/A308https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/707/A308https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/707/A308http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/707/A308GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/707/A308/tablea1 (Observational data, stellar parameters and abundances)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/707/A308/tablea1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/707/A308/tablea1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/707/A308/tablea1?GETtext/xml+votable180.050000true37.01905860.7238040.0055555555555555566/146 342 360 931 1537 2414 3251 3306 3308 3310 3649 3715 4282 4330 4672 4706 4714 4766 4779 5226 5257 5319 5331 5564 5646 5681 5692 5799 5827 5864 5868 5923 6189 6223 6238 6256 6264 6541 6544 6554 6589 6624 7782 7787-7788 8228 8262 8289 8572 8745 8748 8795 8818 8963 8966 9015 9039 9070 9122 9154 9215 9224 9236 9241 9250 9353 9362 9384 9413 9436 9438 9461 9504-9505 9647 9664 9666-9667 9674 9692 9805 9859 9895 9907 9936 9985 10010 10098 10120 10182-10183 10185 10258 10294-10295 10305 10340 10362 10416 10436 10448 10594 10613 10821 10898 10901 10903 10928 10967 11066 11099 11149 11300 11306 11394-11395 11543 11623 11689 11691 11694 11982-11983 11987 12033 12355 12405 12576 12941 13024 14264 14640-14641 14644 14647 14666 14670-14671 14689-14692 14694 14696 14704 14930 15128-15129 15135 15382 15442 15486 16803 17325 17608 18027 18148 18178 18230 18439 18450 18538 18542 18571 18578-18579 18625 18784 19015 19031 19089 19418 19696 19996 22837 22854 22873 23637 23952 24081 24293 25327 25489 25605 25639 25641 25652 25686 25691 25733 25781 25873 25938-25939 26017 26019 26115 26170 26185 26193 26262 26281 26290 26457 26592 26706 26894 27021 27170 27206-27207 27213 27218 27247 27263 27433 27487 27624 27629 27634 27668 27705 27820 27915 28067 28074 28253 28419 28540-28541 28560 28649 28728 28757 28771 28783 28850 28853 28859 28861 28866 28903-28904 29166 29184 29186 29194-29195 29199 29216-29217 29219 29547 29922 29935 30236 30259 30759 30772 30777 31058 31114 31447 32430 32889 32892 32945 32957 33000 33048 33058 33078 33102 33120 33127 33133 33170 33280 33294-33295 33299 33304 33309 33311 33330 33421 33803 33813-33814 33821 33833 33835 33841 33920 35549 35720 36796 37333 37343 37365 37385 37387 37408 37416 37505 37514 37526 37528 37540 37551 37924 37926 37928-37930 38016 38465 38919 38942 39097 39100 41655 42206 42336 42354 42435 42582 42837 42941 42977 42985 42990 43225 43227 44310-44311 44719 44890 44959 45024 46312 46342 46619 46890 47034 47970 47976 48028 48089 48213 48488 49103https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/707/A308?format=asciiInfrareddefaultJ/A+A/707/A308/tablea1Observational data, stellar parameters and abundancesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDR3Gaia DR3 source_id (source_id)meta.id;meta.mainRAJ2000APOGEE right ascensions (J2000) (RA)degpos.eq.ra;meta.mainDEJ2000APOGEE declination (J2000) (DEC)degpos.eq.dec;meta.mainTeffAPOGEE effective temperature (TEFF)Kphys.temperature.effectivedoublee_TeffAPOGEE effective temperature uncertainty (TEFF_ERR)Kstat.error;phys.temperature.effectivedoubleloggAPOGEE surface gravity (LOGG)log(cm.s**-2)phys.gravitydoublee_loggAPOGEE surface gravity uncertainty (LOGG_ERR)log(cm.s**-2)stat.errordoubleFlag[0-3] Visual inspection flag (Flag)meta.code.errorintSample[0/2] Confidence sample flag (Sample)meta.code;src.sampleintS/N? APOGEE signal-to-noise ratio (S/N)stat.snrdoublenullable[M/H]? Weighted metallicity (M_H)phys.abund.Zdoublenullablee_[M/H]? Weighted metallicity uncertainty (M_H_unc)stat.error;phys.abunddoublenullable[Mg/H]? Measured magnesium abundance (Mg_H)phys.abundfloatnullablee_[Mg/H]? Lower magnesium uncertainty (Mg_H_lower)stat.error;phys.abunddoublenullableE_[Mg/H]? Upper magnesium uncertainty (Mg_H_upper)stat.error;stat.maxdoublenullable[Si/H]? Measured sillicon abundance (Si_H)phys.abundfloatnullablee_[Si/H]? Lower silicon uncertainty (Si_H_lower)stat.error;phys.abunddoublenullableE_[Si/H]? Upper silicon uncertainty (Si_H_upper)stat.error;stat.maxdoublenullableHasSpec[*] Has literature metallicity flag (has_spec)meta.codecharRegionKinematic region, dwarf galaxy, or globular cluster (region)src.class.starGalaxy;obs.fieldcharEmpCand[*] Extremely metal-poor star candidate flag (emp_cand)meta.codechar