We present new and accurate near-infrared (NIR) J, K-band time series data for the Galactic globular cluster (GC) M5 = NGC 5904. Data were collected with SOFI at the NTT (71 J+ 120 K images) and with ...NICS at the TNG (25 J+ 22 K images) and cover two orthogonal strips across the centre of the cluster of ≈5 × 10 arcmin2 each. These data allowed us to derive accurate mean K-band magnitudes for 52 fundamental (RR
ab
) and 24 first overtone (RR
c
) RR Lyrae stars. Using this sample of RR Lyrae stars, we find that the slope of the K-band period-luminosity (PLK) relation (−2.33 ± 0.08) agrees quite well with similar estimates available in the literature. We also find, using both theoretical and empirical calibrations of the PLK relation, a true distance to M5 of 14.44 ± 0.02 mag. This distance modulus agrees very well (1σ) with distances based on main-sequence fitting method and on kinematic method (14.44 ± 0.41 mag), while it is systematically smaller than the distance based on the white dwarf cooling sequence (14.67 ± 0.18 mag), even if with a difference slightly larger than 1σ. The true distance modulus to M5 based on the J-band period-luminosity relation (14.50 ± 0.08 mag) is in quite good agreement with the distance based on the PLK relation, further supporting the use of NIR PL relations for RR Lyrae stars to improve the precision of the GC distance scale.
Gaia Early Data Release 3 Riello, M.; De Angeli, F.; Evans, D. W. ...
Astronomy and astrophysics (Berlin),
05/2021, Letnik:
649
Journal Article
Recenzirano
Odprti dostop
Context. Gaia
Early Data Release 3 (
Gaia
EDR3) contains astrometry and photometry results for about 1.8 billion sources based on observations collected by the European Space Agency
Gaia
satellite ...during the first 34 months of its operational phase.
Aims.
In this paper, we focus on the photometric content, describing the input data, the algorithms, the processing, and the validation of the results. Particular attention is given to the quality of the data and to a number of features that users may need to take into account to make the best use of the
Gaia
EDR3 catalogue.
Methods.
The processing broadly followed the same procedure as for
Gaia
DR2, but with significant improvements in several aspects of the blue and red photometer (BP and RP) preprocessing and in the photometric calibration process. In particular, the treatment of the BP and RP background has been updated to include a better estimation of the local background, and the detection of crowding effects has been used to exclude affected data from the calibrations. The photometric calibration models have also been updated to account for flux loss over the whole magnitude range. Significant improvements in the modelling and calibration of the
Gaia
point and line spread functions have also helped to reduce a number of instrumental effects that were still present in DR2.
Results. Gaia
EDR3 contains 1.806 billion sources with
G
-band photometry and 1.540 billion sources with
G
BP
and
G
RP
photometry. The median uncertainty in the
G
-band photometry, as measured from the standard deviation of the internally calibrated mean photometry for a given source, is 0.2 mmag at magnitude
G
= 10–14, 0.8 mmag at
G
≈ 17, and 2.6 mmag at
G
≈ 19. The significant magnitude term found in the
Gaia
DR2 photometry is no longer visible, and overall there are no trends larger than 1 mmag mag
−1
. Using one passband over the whole colour and magnitude range leaves no systematics above the 1% level in magnitude in any of the bands, and a larger systematic is present for a very small sample of bright and blue sources. A detailed description of the residual systematic effects is provided. Overall the quality of the calibrated mean photometry in
Gaia
EDR3 is superior with respect to DR2 for all bands.
Abstract
We present a new complete near-infrared (NIR,
JHK
s
) census of RR Lyrae stars (RRLs) in the globular
ω
Cen (NGC 5139). We collected 15,472
JHK
s
images with 4–8 m class telescopes over 15 ...years (2000–2015) covering a sky area around the cluster center of 60 × 34 arcmin
2
. These images provided calibrated photometry for 182 out of the 198 cluster RRL candidates with 10 to 60 measurements per band. We also provide new homogeneous estimates of the photometric amplitude for 180 (
J
), 176 (
H
) and 174 (
K
s
) RRLs. These data were supplemented with single-epoch
JK
s
magnitudes from VHS and with single-epoch
H
magnitudes from 2MASS. Using proprietary optical and NIR data together with new optical light curves (ASAS-SN) we also updated pulsation periods for 59 candidate RRLs. As a whole, we provide
JHK
s
magnitudes for 90 RRab (fundamentals), 103 RRc (first overtones) and one RRd (mixed-mode pulsator). We found that NIR/optical photometric amplitude ratios increase when moving from first overtone to fundamental and to long-period (
P
> 0.7 days) fundamental RRLs. Using predicted period–luminosity–metallicity relations, we derive a true distance modulus of 13.674 ± 0.008 ± 0.038 mag (statistical error and standard deviation of the median) based on spectroscopic iron abundances, and of 13.698 ± 0.004 ± 0.048 mag based on photometric iron abundances. We also found evidence of possible systematics at the 5%–10% level in the zero-point of the period–luminosity relations based on the five calibrating RRLs whose parallaxes had been determined with the
HST
.
We present the largest near-infrared (NIR) data sets, JHKs, ever collected for classical Cepheids in the Magellanic Clouds (MCs). We selected fundamental (FU) and first overtone (FO) pulsators, and ...found 4150 (2571 FU, 1579 FO) Cepheids for Small Magellanic Cloud (SMC) and 3042 (1840 FU, 1202 FO) for Large Magellanic Cloud (LMC). Current sample is 2-3 times larger than any sample used in previous investigations with NIR photometry. These are consistent with recent results from pulsation models and observations suggesting that the PW relations are minimally affected by the metal content. The new EU and FO PW relations were calibrated using a sample of Galactic Cepheids with distances based on trigonometric parallaxes and Cepheid pulsation models. These new MC distances lead to the relative distance, Delta mu = 0.48 + or - 0.03 mag (FU, log P = 1) and Delta mu = 0.52 + or - 0.03 mag (FO, log P = 0.5), which agrees quite well with previous estimates based on robust distance indicators.
Aims. The iron abundance gradient in the Galactic stellar disk provides fundamental constraints on the chemical evolution of this important Galaxy component, however the spread around the mean slope ...is, at fixed Galactocentric distance, more than the estimated uncertainties. Methods. To provide quantitative constraints on these trends, we adopted iron abundances for 265 classical Cepheids (more than 50% of the currently known sample) based either on high-resolution spectra or on photometric metallicity indices. Homogeneous distances were estimated using near-infrared period-luminosity relations. The sample covers the four disk quadrants, and their Galactocentric distances range from ~5 to ~17 kpc. We provided a new theoretical calibration of the metallicity-index-color (MIC) relation based on Walraven and NIR photometric passbands. Results. We estimated the photometric metallicity of 124 Cepheids. Among them 66 Cepheids also have spectroscopic iron abundances and we found that the mean difference is $-0.03\pm0.15$ dex. We also provide new iron abundances, based on high-resolution spectra, for four metal-rich Cepheids located in the inner disk. The remaining iron abundances are based on high-resolution spectra collected by our group (73) or available in the literature (130). A linear regression over the entire sample provides an iron gradient of $-0.051 \pm 0.004$ dex kpc-1. The above slope agrees quite well, within the errors, with previous estimates based either on Cepheids or on open clusters covering similar Galactocentric distances. However, Cepheids located in the inner disk systematically appear more metal-rich than the mean metallicity gradient. Once we split the sample into inner ($R_{\rm G} <8$ kpc) and outer disk Cepheids, the slope ($-0.130\pm0.015$ dex kpc-1) in the former region is ≈3 times steeper than the slope in the latter one ($-0.042 \pm 0.004$ dex kpc-1). In the outer disk the radial distribution of metal-poor (MP, Fe/H $<-0.02$ dex) and metal-rich (MR) Cepheids across the four disk quadrants does not show a clear trend when moving from the innermost to the external disk regions. The relative fractions of MP and MR Cepheids in the 1st and in the 3rd quadrants differ at the 8σ (MP) and 15σ (MR) levels. Finally, we found that iron abundances in two local overdensities of the 2nd and of the 4th quadrant cover individually a range in iron abundance of ≈0.5 dex. Conclusions. Current findings indicate that the recent chemical enrichment across the Galactic disk shows a clumpy distribution.
Gaia Data Release 3 Montegriffo, P.; De Angeli, F.; Andrae, R. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article
Recenzirano
Odprti dostop
Context.Gaia
Data Release 3 contains astrometry and photometry results for about 1.8 billion sources based on observations collected by the European Space Agency (ESA)
Gaia
satellite during the first ...34 months of its operational phase (the same period covered by
Gaia
early Data Release 3;
Gaia
EDR3). Low-resolution spectra for 220 million sources are one of the important new data products included in this release.
Aims.
In this paper, we focus on the external calibration of low-resolution spectroscopic content, describing the input data, algorithms, data processing, and the validation of the results. Particular attention is given to the quality of the data and to a number of features that users may need to take into account to make the best use of the catalogue.
Methods.
We calibrated an instrument model to relate mean
Gaia
spectra to the corresponding spectral energy distributions (SEDs) using an extended set of calibrators: this includes modelling of the instrument dispersion relation, transmission, and line spread functions. Optimisation of the model is achieved through total least-squares regression, accounting for errors in
Gaia
and external spectra.
Results.
The resulting instrument model can be used for forward modelling of
Gaia
spectra or for inverse modelling of externally calibrated spectra in absolute flux units.
Conclusions.
The absolute calibration derived in this paper provides an essential ingredient for users of
BP
/
RP
spectra. It allows users to connect
BP
/
RP
spectra to absolute fluxes and physical wavelengths.
Gaia Data Release 3 De Angeli, F.; Weiler, M.; Montegriffo, P. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article
Recenzirano
Odprti dostop
Context.
Blue (BP) and Red (RP) Photometer low-resolution spectral data are one of the exciting new products in
Gaia
Data Release 3 (
Gaia
DR3). These data have also been used to derive astrometry ...and integrated photometry in
Gaia
Early Data Release 3 and astrophysical parameters and Solar System object reflectance spectra in
Gaia
DR3.
Aims.
In this paper, we give an overview of the processing techniques that allow raw satellite data of multiple transits per source to be converted into combined spectra calibrated to an internal reference system, resulting in low-resolution BP and RP mean spectra. We describe how we overcome challenges due to the complexity of the on-board instruments and to the various observation strategies. Furthermore, we show highlights from our scientific validation of the results. This work covers the internal calibration of BP/RP spectra to a self-consistent mean instrument, while the calibration of the BP/RP spectra to the absolute reference system of physical flux and wavelength is covered by one of the accompanying
Gaia
DR3 papers.
Methods.
We calibrate about 65 billion individual transit spectra onto the same mean BP/RP instrument through a series of calibration steps, including background subtraction, calibration of the CCD geometry, and an iterative procedure for the calibration of CCD efficiency as well as variations of the line-spread function and dispersion across the focal plane and in time. The calibrated transit spectra are then combined for each source in terms of an expansion into continuous basis functions. We discuss the configuration of these basis functions.
Results.
Time-averaged mean spectra covering the optical to near-infrared wavelength range 330, 1050 nm are published for approximately 220 million objects. Most of these are brighter than
G
= 17.65 but some BP/RP spectra are published for sources down to
G
= 21.43. Their signal-to-noise ratio (S/N) varies significantly over the wavelength range covered, and with magnitude and colour of the observed objects, with sources around
G
= 15 having a S/N above 100 in some wavelength ranges. The top-quality BP/RP spectra are achieved for sources with magnitudes 9 <
G
< 12, with S/N reaching 1000 in the central part of the RP wavelength range. Scientific validation suggests that the internal calibration was generally successful. However, there is some evidence for imperfect calibrations at the bright end
G
< 11, where calibrated BP/RP spectra can exhibit systematic flux variations that exceed their estimated flux uncertainties. We also report that, due to long-range noise correlations, BP/RP spectra can exhibit wiggles when sampled in pseudo-wavelength.
Conclusions.
The
Gaia
DR3 data products are the expansion coefficients and corresponding covariance matrices for BP and RP separately. Users are encouraged to work with the data in this format, with full covariance information showing that correlations between coefficients are typically very low. Documentation and instructions on how to access and use BP/RP spectral data from the archive are also provided.
We present near-infrared (NIR) J-, H-, and K-band time series observations of the Galactic globular cluster (GGC) M92. On the basis of these data, we derive well-sampled light curves for 11 out of ...the 17 cluster RR Lyrae variables and, in turn, accurate mean NIR magnitudes. The comparison between the predicted and empirical slopes of the NIR period-luminosity (PL) relations indicates a very good agreement. Cluster distance determinations based on independent theoretical NIR PL relations present uncertainties smaller than 5% and agree quite well with recent distance estimates based on different distance indicators. We also obtain accurate and deep NIR color-magnitude diagrams ranging from the tip of the red giant branch (RGB) down to the main-sequence turnoff. We detect the RGB bump, and the NIR luminosities of this evolutionary feature are, within theoretical and empirical uncertainties, in good agreement with each other.
We present new intermediate-band Stromgren photometry based on more than 300 u, v, b, y images of the Galactic globular cluster omega Cen. Optical data were supplemented with new multiband ...near-infrared (NIR) photometry (350 J, H, Ks images). The final optical-NIR catalog covers a region of more than 20 X 20 arcmin squared across the cluster center. We use different optical-NIR color-color planes together with proper-motion data available in the literature to identify candidate cluster red-giant (RG) stars. By adopting different Stromgren metallicity indices, we estimate the photometric metallicity for 4000 RGs, the largest sample ever collected. The metallicity distributions show multiple peaks (Fe/Hphot = -1.73 +/- 0.08, -1.29 +/- 0.03, -1.05 +/- 0.02, -0.80 +/- 0.04, -0.42 +/- 0.12, and -0.07 +/- 0.08 dex) and a sharp cutoff in the metal-poor (MP) tail (Fe/Hphot -2 dex) that agree quite well with spectroscopic measurements. We identify four distinct subpopulations, namely, MP (Fe/H < = -1.49), metal-intermediate (MI; -1.49 < Fe/H < = -0.93), metal-rich (MR; -0.95 < Fe/H < = -0.15), and solar metallicity (Fe/H 0). The last group includes only a small fraction of stars (~8% +/- 5%) and should be confirmed spectroscopically. Moreover, using the difference in metallicity based on different photometric indices, we find that the 19% +/- 1% of RGs are candidate CN-strong stars. This fraction agrees quite well with recent spectroscopic estimates and could imply a large fraction of binary stars. The Stromgren metallicity indices display a robust correlation with alpha-elements (Ca+Si/H) when moving from the MI to the MR regime (Fe/H -1.7 dex).
Gaia Data Release 2 Evans, D. W.; Riello, M.; De Angeli, F. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
Aims.
We describe the photometric content of the second data release of the
Gaia
project (
Gaia
DR2) and its validation along with the quality of the data.
Methods.
The validation was mainly carried ...out using an internal analysis of the photometry. External comparisons were also made, but were limited by the precision and systematics that may be present in the external catalogues used.
Results.
In addition to the photometric quality assessment, we present the best estimates of the three photometric passbands. Various colour-colour transformations are also derived to enable the users to convert between the
Gaia
and commonly used passbands.
Conclusions.
The internal analysis of the data shows that the photometric calibrations can reach a precision as low as 2 mmag on individual CCD measurements. Other tests show that systematic effects are present in the data at the 10 mmag level.
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