Using classical Cepheids to study the far side of the Milky Way disk: I. Spectroscopic classification and the metallicity gradient

Abstract

The structure, kinematics, and chemical composition of the far side of the Milky Way disk, beyond the bulge, are still to be revealed. Classical Cepheids (CCs) are young and luminous standard candles. We aim to use a well-characterized sample of these variable stars to study the present time properties of the far side of the Galactic disk. A sample of 45 Cepheid variable star candidates were selected from near infrared time series photometry obtained by the VVV survey. We characterized this sample using high quality near infrared spectra obtained with VLT/X-Shooter, deriving radial velocities and iron abundances for all the sample Cepheids. This allowed us to separate the CCs, which are metal rich and with kinematics consistent with the disk rotation, from type II Cepheids (T2Cs), which are more metal poor and with different kinematics. We estimated individual distances and extinctions using VVV photometry and period-luminosity relations, reporting the characterization of 30 CCs located on the far side of the Galactic disk, plus 8 T2Cs mainly located in the bulge region, of which 10 CCs and 4 T2Cs are new discoveries. This is the first sizeable sample of CCs in this distant region of our Galaxy that has been spectroscopically confirmed. We use their positions, kinematics, and metallicities to confirm that the general properties of the far disk are similar to those of the well-studied disk on the solar side of the Galaxy. In addition, we derive for the first time the radial metallicity gradient on the disk's far side. Considering all the CCs with $R_{\mathrm{GC}}<17\mathrm{kpc}$, we measure a gradient with a slope of $-0.062\mathrm{dex}\mathrm{kp}{\mathrm{c}}^{-1}$ and an intercept of $+0.59\mathrm{dex}$, which is in agreement with previous determinations based on CCs on the near side of the disk.

arXiv comment16 pages, 10 figures, accepted for publication in Astronomy & Astrophysics

References in corpus (63)

• Astropy: A Community Python Package for Astronomy
• SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• GLIMPSE: I. A SIRTF Legacy Project to Map the Inner Galaxy
• X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope
• VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way
• Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• A distance to the Large Magellanic Cloud that is precise to one per cent
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• Vertical waves in the solar neighbourhood in Gaia DR2
• A Spectroscopic Study of the Ancient Milky Way: F- and G-Type Stars in the Third Data Release of the Sloan Digital Sky Survey
• Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red Clump Stars
• Interstellar Extinction Law toward the Galactic Center III: J, H, Ks bands in the 2MASS and the MKO systems, and 3.6, 4.5, 5.8, 8.0 micron in the Spitzer/IRAC system
• New ATLAS9 And MARCS Model Atmosphere Grids for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Interstellar Extinction Law in the J, H, and Ks Bands toward the Galactic Center
• The Distribution of the Elements in the Galactic Disk III. A Reconsideration of Cepheids from l = 30 to 250 Degrees
• The influence of chemical composition on the properties of Cepheid stars. II-The iron content
• Chemodynamical history of the Galactic Bulge
• On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk
• A three-dimensional map of the Milky Way using classical Cepheid variable stars
• The SDSS-III APOGEE Spectral Line List for H-band Spectroscopy
• Classical Cepheid Pulsation Models. X. The Period-Age Relation
• The GIRAFFE Inner Bulge Survey (GIBS) III. Metallicity distributions and kinematics of 26 Galactic bulge fields
• Rotation curve of the Milky Way from Classical Cepheids
• Red giants observed by CoRoT and APOGEE: The evolution of the Milky Way's radial metallicity gradient
• The VISTA ZYJHKs Photometric System: Calibration from 2MASS
• VVV Survey Near-Infrared Photometry of Known Bulge RR Lyrae stars: the Distance to the Galactic Center and Absence of a Barred Distribution of the Metal-Poor Population
• Classical Cepheid Pulsation Models. III. The Predictable Scenario
• Stellar density profile and mass of the Milky Way Bulge from VVV data
• Cepheid pulsation models at varying metallicity and DY/DZ
• The X-shooter Spectral Library (XSL): I. DR1. Near-ultraviolet through optical spectra from the first year of the survey
• Three classical Cepheid variable stars in the nuclear bulge of the Milky Way
• Large Magellanic Cloud Near-Infrared Synoptic Survey. I. Cepheid variables and the calibration of the Leavitt Law
• Extinction ratios in the inner Galaxy as revealed by the VVV survey
• Mean JHK Magnitudes of Fundamental-Mode Cepheids from Single-Epoch Observations
• Baade-Wesselink distances to Galactic and Magellanic Cloud Cepheids and the effect of metallicity
• Field Stars and Clusters of the Galactic Bulge: Implications for Galaxy Formation
• The panchromatic view of the Magellanic Clouds from Classical Cepheids. I. Distance, Reddening and Geometry of the Large Magellanic Cloud disk
• Abundances in the Local Region I: G and K Giants
• New NIR light-curve templates for classical Cepheids
• The Chemical Compositions of Non-Variable Red and Blue Field Horizontal Branch Stars
• Large Magellanic Cloud Near-Infrared Synoptic Survey. IV. Leavitt Laws for Type II Cepheid Variables
• A lack of classical Cepheids in the inner part of the Galactic disk
• The VVV Survey reveals classical Cepheids tracing a young and thin stellar disk across the Galaxy's bulge
• Mapping the stellar age of the Milky Way bulge with the VVV. I. The method
• Constraining Dust Extinction Properties via the VVV Survey
• A new near-IR window of low extinction in the Galactic plane
• Proper motions in the VVV Survey: Results for more than 15 million stars across NGC 6544
• Kinematics of classical Cepheids in the Nuclear Stellar Disk
• On the optimal calibration of VVV photometry
• Milky Way metallicity gradient from Gaia DR2 F/1O double-mode Cepheids
• The Calcium Triplet metallicity calibration for galactic bulge stars
• A Near-infrared RR Lyrae census along the southern Galactic plane: the Milky Way's stellar fossil brought to light
• Chemical compositions of thin-disk, high-metallicity red horizontal-branch field stars
• Into the Darkness: Classical and Type II Cepheids in the Zona Galactica Incognita
• Structure and kinematics of Type II Cepheids in the Galactic bulge based on near-infrared VVV data
• First metallicity determination from Near-Infrared spectra for five obscured Cepheids discovered in the inner Disk
• On a new and homogeneous metallicity scale for Galactic classical Cepheids - I. Physical parameters
• Discovery of a Pair of Classical Cepheids in an Invisible Cluster Beyond the Galactic Bulge
• New Galactic Star Clusters Discovered in the Disk Area of the VVVX Survey
• Metallicity Distribution of Disk Stars and the Formation History of the Milky Way
• New classical Cepheids in the inner part of the northern Galactic disk and their kinematics

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• Open clusters housing classical Cepheids in Gaia DR3
• The VVV survey: Long-period variable stars I. Photometric catalog of ten VVV/OGLE tiles
• Cepheid Metallicity in the Leavitt Law (C- MetaLL) survey: VI: Radial abundance gradients of 29 chemical species in the Milky Way Disk
• Metallicity estimation of MW, SMC and LMC classical Cepheids from the shape of the $V$- and $I$-band light curves
• A new distance to the Brick, the dense molecular cloud G0.253+0.016
• Comparing bulge RR Lyrae stars with bulge giants -- Insight from 3D kinematics
• Line-depth ratios as indicators of effective temperature and surface gravity
• A high resolution study of near-IR diffuse interstellar bands, search for small scale structure, time variability and stellar features
• VVV catalog of ab-type RR Lyrae in the inner Galactic bulge
• Investigating stellar variability in the open cluster region NGC 381
• Unveiling VVV/WISE Mira variables on the far side of the Galactic disk: Distances, kinematics and a new extinction law
• Open clusters in the outer disc studied with MEGARA@GTC Auner 1 and Berkeley 102
• Near-IR CO and CN in classical Cepheids
• Effects of metallicity on mode switching in Cepheids
• Spectroscopic analysis of VVV CL001 cluster with MUSE