APASS BVgri search for and characterization of RR Lyr variables candidate members of the Aquarius halo stream

Munari, U.; Henden, A. A.; Frigo, A.

doi:10.1016/j.newast.2013.07.007

Cited by 51 publications

(66 citation statements)

References 18 publications

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“…We adopt the photometry from Munari et al (2014), and extinction in the V-band, A V , is computed using the coefficients in Schlafly & Finkbeiner (2011). Bolometric corrections are taken from Casagrande & VandenBerg (2014).…”

Section: Observations and Stellar Parametersmentioning

confidence: 99%

Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and 〈3D〉 Models. II. Chemical Properties of the Galactic Metal-poor Disk and the Halo

Bergemann

Collet

Schönrich

et al. 2017

ApJ

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From exploratory studies and theoretical expectations it is known that simplifying approximations in spectroscopic analysis (LTE, 1D) lead to systematic biases of stellar parameters and abundances. These biases depend strongly on surface gravity, temperature, and, in particular, for LTE vs. non-LTE (NLTE) on metallicity of the stars. Here we analyse the [Mg/Fe] and [Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained using 1D hydrostatic models and averaged 3D models. We show that compared to the 3D NLTE benchmark, all other three methods display increasing biases towards lower metallicities, resulting in false trends of [Mg/Fe] against [Fe/H], which have profound implications for interpretations by chemical evolution models. In our best 3D NLTE model, the halo and disc stars show a clearer behaviour in the [Mg/Fe] − [Fe/H] plane, from the knee in abundance space down to the lowest metallicities. Our sample has a large fraction of thick disc stars and this population extends down to at least [Fe/H] ∼ −1.6 dex, further than previously proven. The thick disc stars display a constant [Mg/Fe] ≈ 0.3 dex, with a small intrinsic dispersion in [Mg/Fe] that suggests that a fast SN Ia channel is not relevant for the disc formation. The halo stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the diverse origin of halo stars from accreted low-mass systems to stochastic/inhomogeneous chemical evolution in the Galactic halo.

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Section: Observations and Stellar Parametersmentioning

confidence: 99%

Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and 〈3D〉 Models. II. Chemical Properties of the Galactic Metal-poor Disk and the Halo

Bergemann

Collet

Schönrich

et al. 2017

ApJ

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“…It is interesting to note that the spectroscopically derived effective temperature difference between the two stars is in good agreement with the result obtained from photometric measurements. In fact, following the same analysis performed by Munari et al (2014) for half a million stars of the RAVE spectroscopic survey, if we assume a colour excess of E(B − V) = 0.02 mag (as explained in Sect. 3.3) the XO-2S star is 60 ± 33 K hotter than the companion.…”

Section: Spectroscopic Analysis Of the Individual Starsmentioning

confidence: 99%

The GAPS programme with HARPS-N at TNG

Damasso

Biazzo

Bonomo

et al. 2015

A&A

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Aims. XO-2 is the first confirmed wide stellar binary system where the almost twin components XO-2N and XO-2S have planets, and it is a peculiar laboratory in which to investigate the diversity of planetary systems. This stimulated a detailed characterization study of the stellar and planetary components based on new observations. Methods. We collected high-resolution spectra with the HARPS-N spectrograph and multi-band light curves. Spectral analysis led to an accurate determination of the stellar atmospheric parameters and characterization of the stellar activity, and high-precision radial velocities of XO-2N were measured. We collected 14 transit light curves of XO-2Nb used to improve the transit parameters. Photometry provided accurate magnitude differences between the stars and a measure of their rotation periods. Results. The iron abundance of XO-2N was found to be +0.054 dex greater, within more than 3σ, than that of XO-2S. The existence of a longterm variation in the radial velocities of XO-2N is confirmed, and we detected a turnover with respect to previous measurements. We suggest the presence of a second massive companion in an outer orbit or the stellar activity cycle as possible causes of the observed acceleration. The latter explanation seems more plausible with the present dataset. We obtained an accurate value of the projected spin-orbit angle for the XO-2N system (λ = 7• ± 11 • ), and estimated the real 3D spin-orbit angle (ψ = 27 +12 −27 degrees). We measured the XO-2 rotation periods, and found a value of P = 41.6 ± 1.1 days in the case of XO-2N, in excellent agreement with the predictions. The period of XO-2S appears shorter, with an ambiguity between 26 and 34.5 days that we cannot solve with the present dataset alone. The analysis of the stellar activity shows that XO-2N appears to be more active than the companion, perhaps because we sampled different phases of their activity cycle, or because of an interaction between XO-2N and its hot Jupiter that we could not confirm.

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“…Stars in the RAVE catalog were also observed by the AAVSO Photometric All-Sky Survey (APASS, Munari et al 2014) in four visual and one near-infrared band. Spectral ranges deeper in the infrared domain were covered by DENIS, 2MASS, and WISE.…”

Section: Methodsmentioning

confidence: 99%

Very Metal-poor Stars Observed by the RAVE Survey

Matijevič

2015

Proc. IAU

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Metal-poor stars trace the earliest phases in the chemical enrichment of the Universe. They give clues about the early assembly of the Galaxy as well as on the nature of the first stellar generations. Multi-object spectroscopic surveys play a key role in finding these fossil records in large volumes. Here we present a novel analysis of the metal-poor star sample in the complete Radial Velocity Experiment (RAVE) Data Release 5 catalog with the goal of identifying and characterizing all very metal-poor stars observed by the survey. Using a three-stage method, we first identified the candidate stars using only their spectra as input information. We employed an algorithm called t-SNE to construct a low-dimensional projection of the spectrum space and isolate the region containing metal-poor stars. Following this step, we measured the equivalent widths of the near-infrared Ca ii triplet lines with a method based on flexible Gaussian processes to model the correlated noise present in the spectra. In the last step, we constructed a calibration relation that converts the measured equivalent widths and the color information coming from the 2MASS and WISE surveys into metallicity and temperature estimates. We identified 877 stars with at least a 50% probability of being very metal-poor ([Fe/H] < −2 dex), out of which 43 are likely extremely metal-poor ([Fe/H] < −3 dex). The comparison of the derived values to a small subsample of stars with literature metallicity values shows that our method works reliably and correctly estimates the uncertainties, which typically have values σ [Fe/H] ≈ 0.2 dex. In addition, when compared to the metallicity results derived using the RAVE DR5 pipeline, it is evident that we achieve better accuracy than the pipeline and therefore more reliably evaluate the very metal-poor subsample. Based on the repeated observations of the same stars, our method gives very consistent results. We intend to study the identified sample further by acquiring high-resolution spectroscopic follow-up observations. The method used in this work can also easily be extended to other large-scale data sets, including to the data from the Gaia mission and the upcoming 4MOST survey.

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APASS BVgri search for and characterization of RR Lyr variables candidate members of the Aquarius halo stream

Cited by 51 publications

References 18 publications

Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and 〈3D〉 Models. II. Chemical Properties of the Galactic Metal-poor Disk and the Halo

Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and 〈3D〉 Models. II. Chemical Properties of the Galactic Metal-poor Disk and the Halo

The GAPS programme with HARPS-N at TNG

Very Metal-poor Stars Observed by the RAVE Survey

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