Gaia Data Release 1

Abstract

Context. Parallaxes for 331 classical Cepheids, 31 Type II Cepheids, and 364 RR Lyrae stars in common between Gaia and the Hipparcos and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). Aims. In order to test these first parallax measurements of the primary standard candles of the cosmological distance ladder, which involve astrometry collected by Gaia during the initial 14 months of science operation, we compared them with literature estimates and derived new period-luminosity (PL), period-Wesenheit (PW) relations for classical and Type II Cepheids and infrared PL, PL-metallicity (PLZ), and optical luminosity-metallicity (M V -[Fe/H]) relations for the RR Lyrae stars, with zero points based on TGAS. Methods. Classical Cepheids were carefully selected in order to discard known or suspected binary systems. The final sample comprises 102 fundamental mode pulsators with periods ranging from 1.68 to 51.66 days (of which 33 with σ / < 0.5). The Type II Cepheids include a total of 26 W Virginis and BL Herculis stars spanning the period range from 1.16 to 30.00 days (of which only 7 with σ / < 0.5). The RR Lyrae stars include 200 sources with pulsation period ranging from 0.27 to 0.80 days (of which 112 with σ / < 0.5). The new relations were computed using multi-band (V, I, J, K s ) photometry and spectroscopic metal abundances available in the literature, and by applying three alternative approaches: (i) linear least-squares fitting of the absolute magnitudes inferred from direct transformation of the TGAS parallaxes; (ii) adopting astrometrybased luminosities; and (iii) using a Bayesian fitting approach. The last two methods work in parallax space where parallaxes are used directly, thus maintaining symmetrical errors and allowing negative parallaxes to be used. The TGAS-based PL, PW, PLZ, and M V − [Fe/H] relations are discussed by comparing the distance to the Large Magellanic Cloud provided by different types of pulsating stars and alternative fitting methods. A79, page 2 of 29Gaia Collaboration (Clementini, G., et al.): Gaia Data Release 1Results. Good agreement is found from direct comparison of the parallaxes of RR Lyrae stars for which both TGAS and HST measurements are available. Similarly, very good agreement is found between the TGAS values and the parallaxes inferred from the absolute magnitudes of Cepheids and RR Lyrae stars analysed with the Baade-Wesselink method. TGAS values also compare favourably with the parallaxes inferred by theoretical model fitting of the multi-band light curves for two of the three classical Cepheids and one RR Lyrae star, which were analysed with this technique in our samples. The K-band PL relations show the significant improvement of the TGAS parallaxes for Cepheids and RR Lyrae stars with respect to the Hipparcos measurements. This is particularly true for the RR Lyrae stars for which improvement in quality and statistics is impressive. Conclusions. TGAS parallaxes bring a significant added value t...

Is Terzan 5 the remnant of a building block of the Galactic bulge? Evidence from APOGEE

“…The focus on the NIR is essential to investigate stars located in the Galactic disc and bulge due to the high extinction caused by intervening dust. We use atmospheric parameters, elemental abundances, and quality flags for stars from APOGEE 2, based on the automatic analysis of its spectra performed by the APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP; García Pérez et al 2016;Holtzman et al 2015Holtzman et al , 2018Jönsson et al 2020) 1 , and stellar distances provided by an astroNN neural network trained on stars with APOGEE spectra and Gaia EDR3 (Gaia Collaboration et al 2016Collaboration et al , 2017 parallax measurements (Leung & Bovy 2019a,b).…”

V680 Mon -- a young mercury-manganese star in an eclipsing heartbeat system

“…Despite these results, and the correct identification of the star as an eclipsing binary in the International Variable Star Index (VSX; Watson 2006) of the American Association of Variable Star Observers (AAVSO), the star has been listed as an RR Lyrae variable in the SIMBAD database (Wenger et al 2000) until recently, which is probably the reason why it was included into the samples of the RR-Lyrae-star-based studies of Gavrilchenko et al (2014) and Gaia Collaboration et al (2017). On the initiative of the present authors, V680 Mon is now correctly identified in the SIMBAD database as an eclipsing binary star.…”

Astronomical distance scales

“…The population is rather uniform and the basic assumption is that Cepheids in external galaxies behave like those found in the Milky Way. The Gaia DR2 variability set comprises 9675 stars classifieds as Cepheids, against only 599, mainly in the region of the LMC, in the DR1 [33]. This represents the first full-sky census of Cepheids and provides a flavour of Gaia potential to recover most of the Milky Way Cepheids [34], not hidden by dust clouds.…”