EFEBHO catalogs
The major breakthrough of EFEBHO is the unique opportunity to use ancillary spectroscopic and photometric datasets for Halo, Bulge, nearby dwarf galaxy and GC RRLs.
Stellar variability is living a golden age thanks to several ongoing long-term optical (OGLEIV, Dark Energy Survey, Gaia) and mid-infrared (MIR, NeoWISE) photometric surveys.
The next Gaia mission data release (DR3) will provide homogeneous photometry in three bands for hundreds of thousands RR Lyrae variable stars belonging to all the Galactic components. In particular, this data will allow us to study the Halo up to ~100 kpc as well as almost all the GCs and the majority of the dwarf galaxies satellite of the MW. Radial velocities will also be available for stars with G~16 mag, that is up to about 11-12 kpc from the Sun. Our group collected literature optical, NIR and MIR photometry for ~200,000 Halo RRLs (see Fig. 1). Furthermore, we have been awarded more than six months of observing time (in five years) to collect simultaneous JHK-band, time-series data of ~250 field and cluster RRLs with the Japanese observing facility (SIRIUS@IRSF, SAAO) These RRLs are the perfect calibrators to derive new empirical PLZ relations fully rooted on geometrical distances (Gaia) and accurate photometric and spectroscopic measurements.
We are involved in a long-term project aimed at investigating the impact of the environment on stellar pulsation properties. We are providing a complete census of radial variables in nearby dwarf spheroidals (dSphs: Carina, Sculptor, Fornax, LeoI,II, Tucana, Cetus, Canes Venatici I, Crater II; Monelli+17) and ultra faint dwarfs (Bootes I, Hercules, Leo IV, Canes Venatici II, Coma, Ursa Minor I,II; Musella+12, Dall’Ora+12). To date, we have reduced several thousands (proprietary plus literature) images collected with ground- and space-based facilities, for two dSphs (Draco, Ursa Minor). These datasets will probe the role that major/minor mergers played in building up the Halo. The cluster RRL catalogs are based on proprietary and literature data (e.g. Braga+16, Mullen+21). Bulge: Ongoing optical (OGLE IV, Pietrukowicz+15) and NIR (VVV/VVV-X, Minniti+16) surveys have provided a complete census of RRLs in the outer Bulge and in low-reddening regions. However, they are incomplete in the innermost Galactic regions due to the high reddening. We have been awarded ~1500 hours (2 large programs) with SPITZER to collect MIR time-series of RRLs in the Bulge and in nearby stellar systems. Note that MIR magnitudes ([3.6 μm], [4.5 μm]) are ~25 times less affected than optical magnitudes by reddening uncertainties. These data will allow us to estimate Bulge RRL distances with an accuracy better than 3%.
RRLs have periods ranging from 0.2 to 1 day, they experience rapid atmospheric changes along the pulsation cycle and chemical abundance investigations might be difficult. Thanks to large telescopes, the exposure times decreased to a few minutes, thus allowing detailed studies of the atmospheric phenomena in field and cluster RRLs (Pancino+15, Sneden+17; Magurno+19). These investigations confirmed that nonlinear phenomena (shocks) are restricted to a very narrow window of a few tens of minutes, thus paving the way to random phase observations for accurate RRL abundance determinations.
HIGH RESOLUTION (HR)- Our group started a long-term observing campaign to secure a large sample of HR (R ≳ 30,000) and high SNR spectra (≳ 50) (Crestani+21, Gilligan+21) for 247 RRLs. They were collected with HR spectrographs (FEROS@2.2m MPG, HARPS@3.6m, UVES@VLT, HARPS-N@TNG, DuPont, MIKE@MAGELLAN, HRS@SALT, HDS@SUBARU).
LOW RESOLUTION (LR)- HR spectroscopy is still a resource-consuming endeavor. To trace the structure of the entire Halo we need diagnostics based on LR spectra. We performed a new calibration of the Delta S method (Preston59) in which the equivalent widths of the CaII K line and three Balmer lines (Hβ, Hγ, Hδ) provide an estimate of individual RRL metallicities. The new calibration is rooted on ~143 field RRLs with Fe abundances based on HR spectra covering three dex in iron conten (-2.8 ≲ [Fe/H] ≲ 0.2) and including for the first time both fundamental (RRab) and first-overtone (RRc) RRLs (Crestani+21). The new calibration was also applied to SDSS and LAMOST LR spectra for field RRLs. We ended up with more than 9300 (~8100 our + literature) RRLs for which we have homogeneous iron abundance estimates (see Figs. 1, 2).
RADIAL VELOCITIES- The measurement of the RRL barycentric radial velocity ( -velocity) also requires multiple measurements to trace the variation along the pulsation cycle. To overcome these demanding observations our group secured more than 16,000 LR and HR spectra (proprietary plus literature) of field RRLs (Bono+20). We have already derived radial velocity templates for both RRab and RRc (Prudil+21). Using these templates, EFEBHO will provide γ- velocities on the basis of individual measurements once period, luminosity amplitude and epoch of maximum light are known (~9000 RRLs).
We have already secured LR spectra, collected with VIMOS@VLT. We were awarded 6 nights and succeeded in collecting LR spectra for ~1000 Bulge RRLs. These spectra will allow us to estimate not only the γ-velocity, but also individual metallicities (Delta S method). Note that, to provide a detailed abundance analysis (alpha, neutron capture elements) we have also collected several hundreds of HR spectra for Baade window RRLs by using the multi-object fiber spectrograph GIRAFFE/FLAMES@VLT.