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Colour-colour diagram using SDSS synthetic photometry for both catalogues. NGSL stars are red dots while MAW stars are shown as blue dots. We draw a 1 Myr theoretical PARSEC curve with solar metallicity and no extinction. Black triangles represent main stellar locus in SDSS photometry from Covey et al. (2007).
Source publication
This paper describes the characterization of the GALANTE photometric system, a seven intermediate- and narrow-band filter system with a wavelength coverage from 3000 $\r{A}$ to 9000 $\r{A}$ . We describe the photometric system presenting the full sensitivity curve as a product of the filter sensitivity, CCD, telescope mirror, and atmospheric transm...
Contexts in source publication
Context 1
... obtain synthetic photometric GALANTE and SDSS AB magnitudes for NGSL and MAW libraries using the response curves shown in Figure 2. Figure 5 shows a colour-colour diagram for both catalogues. NGSL stars are represented by red dots while MAW stars are shown in blue dots. ...
Context 2
... at both catalogues in this figure one can see that the MAW library covers a good number of reddened high-temperature stars, showing a sparse distribution for dwarf late-type and giant stars, whereas the NGSL library covers a wider range of temperature and gravity but is limited in reddening. Lastly, in order to derive GALANTE transformation equations that are as general as possible, we use both catalogues as a single one to better probe the diagram of Figure 5. ...
Context 3
... obtain synthetic photometric GALANTE and SDSS AB magnitudes for NGSL and MAW libraries using the response curves shown in Figure 2. Figure 5 shows a colour-colour diagram for both catalogues. NGSL stars are represented by red dots while MAW stars are shown in blue dots. ...
Context 4
... at both catalogues in this figure one can see that the MAW library covers a good number of reddened high-temperature stars, showing a sparse distribution for dwarf late-type and giant stars, whereas the NGSL library covers a wider range of temperature and gravity but is limited in reddening. Lastly, in order to derive GALANTE transformation equations that are as general as possible, we use both catalogues as a single one to better probe the diagram of Figure 5. ...
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Citations
... Furthermore, those four filters are designed to avoid the Balmer lines and, in that way, measure the stellar continuum for OBA stars. In that way, GALANTE photometry can be used to build Bracket-like diagrams (Lorenzo-Gutiérrez et al. 2019) analogous to those used in the Strömgren system and simultaneously measure eff , (4405 − 5495), and 5495 for hot stars and metallicity for cool ones. ...
The GALANTE optical photometric survey is observing the northern Galactic plane and some adjacent regions using seven narrow- and intermediate-filters, covering a total of 1618 square degrees. The survey has been designed with multiple exposure times and at least two different air masses per field to maximize its photometric dynamic range, comparable to that of Gaia, and ensure the accuracy of its photometric calibration. The goal is to reach at least 1% accuracy and precision in the seven bands for all stars brighter than AB magnitude 17 while detecting fainter stars with lower values of the signal-to-noise ratio.The main purposes of GALANTE are the identification and study of extinguished O+B+WR stars, the derivation of their extinction characteristics, and the cataloguing of F and G stars in the solar neighbourhood. Its data will be also used for a variety of other stellar studies and to generate a high-resolution continuum-free map of the H{\alpha} emission in the Galactic plane. We describe the techniques and the pipeline that are being used to process the data, including the basis of an innovative calibration system based on Gaia DR2 and 2MASS photometry.
... • Study the optical extinction law combining Gaia data with the GALANTE photometric survey (Maíz Apellániz et al. 2019;Lorenzo-Gutiérrez et al. 2019) and other deep surveys of the Galactic plane. ...
We have started an ambitious program to determine if the full diversity of extinction laws is real or if some of it is due to calibration or methodological issues. Here we start by analysing the information on near-infrared (NIR) extinction in a Two Micron All-Sky Survey (2MASS) stellar sample with good quality photometry and very red colours. We calculate the extinction at 1 μm, A1, and the power-law exponent, α (Aλ = A1λ−α), for the 2MASS stars located in the extinction trajectory in the H − K versus J − H plane expected for red giants with A1 > 5 mag. We test the validity of the assumption about the nature of those stars, whether a single or multiple values of α are needed, and the spatial variations of the results. Most (∼83 per cent) of those stars can indeed be explained by high-extinction red giants and the rest are composed of extinguished asymptotic giant branch (AGB) stars (mostly O-rich), blended sources, and smaller numbers of other objects, a contaminant fraction that can be reduced with the help of Gaia Data Release 2 (DR2) data. Galactic red giants experience a NIR extinction with α ∼ 2.27 and an uncertainty of a few hundredths of a magnitude. There is no significant spread in α even though our sample is widely distributed and has a broad range of extinctions. Differences with previous results are ascribed to the treatment of non-linear photometric effects and/or the contaminant correction. Future research should concentrate in finding the correct functional form for the NIR extinction law. In the appendix, we detail the treatment of non-linear photometric effects in the 2MASS bands.
... The North America and Pelican nebulae as imaged by the GALANTE survey(Maíz Apellániz et al. 2019a;Lorenzo-Gutiérrez et al. 2019). The Bajamar star, responsible for most of the ionizing photons, is the red object indicated by the arrow, hidden behind the molecular cloud that creates the Atlantic Ocean and Gulf of Mexico and that also obscures the unseen nebulosity and background stars. ...
We have detected a broad interstellar absorption band centred close to 7700 \r{A} and with a FWHM of 176.6$\pm$3.9 \r{A}. This is the first such absorption band detected in the optical range and is significantly wider than the numerous diffuse interstellar bands (DIBs). It remained undiscovered until now because it is partially hidden behind the A telluric band produced by O$_2$. The band was discovered using STIS@HST spectra and later detected in a large sample of stars of diverse type (OB stars, BA supergiants, red giants) using further STIS and ground-based spectroscopy. The EW of the band is measured and compared with our extinction and K I $\lambda\lambda$7667.021,7701.093 measurements for the same sample. The carrier is ubiquitous in the diffuse and translucent Galactic ISM but is depleted in the environment around OB stars. In particular, it appears to be absent or nearly so in sightlines rich in molecular carbon. This behaviour is similar to that of the $\sigma$-type DIBs, which originate in the low/intermediate-density UV-exposed ISM but are depleted in the high-density UV-shielded molecular clouds. We also present an update on our previous work on the relationship between $E(4405-5495)$ and $R_{5495}$ and incorporate our results into a general model of the ISM.
... • Study the optical extinction law combining Gaia data with the GALANTE photometric survey (Maíz Apellániz et al. 2019;Lorenzo-Gutiérrez et al. 2019) and other deep surveys of the Galactic plane. ...
We have started an ambitious program to determine if the full diversity of extinction laws is real or if some of it is due to calibration or methodological issues. Here we start by analyzing the information on NIR extinction in a 2MASS stellar sample with good quality photometry and very red colours. We calculate the extinction at 1 $\mu$m, $A_1$, and the power-law exponent, $\alpha$ ($A_\lambda = A_1 \lambda^{-\alpha}$), for the 2MASS stars located in the extinction trajectory in the $H-K$ vs. $J-H$ plane expected for red giants with $A_1 > 5$ mag. We test the validity of the assumption about the nature of those stars, whether a single or multiple values of $\alpha$ are needed, and the spatial variations of the results. Most ($\sim$83%) of those stars can indeed be explained by high-extinction red giants and the rest is composed of extinguished AGB stars (mostly O-rich), blended sources, and smaller numbers of other objects, a contaminant fraction that can be reduced with the help of Gaia} DR2 data. Galactic red giants experience a NIR extinction with $\alpha\sim 2.27$ and an uncertainty of a few hundredths of a magnitude. There is no significant spread in $\alpha$ even though our sample is widely distributed and has a broad range of extinctions. Differences with previous results are ascribed to the treatment of non-linear photometric effects and/or the contaminant correction. Future research should concentrate in finding the correct functional form for the NIR extinction law. In the appendix we detail the treatment of non-linear photometric effects in the 2MASS bands.
The GALANTE optical photometric survey is observing the northern Galactic plane and some adjacent regions using seven narrow- and intermediate-filters, covering a total of 1618 deg2. The survey has been designed with multiple exposure times and at least two different air masses per field to maximize its photometric dynamic range, comparable to that of Gaia, and ensure the accuracy of its photometric calibration. The goal is to reach at least 1 per cent accuracy and precision in the seven bands for all stars brighter than AB magnitude 17 while detecting fainter stars with lower values of the signal-to-noise ratio. The main purposes of GALANTE are the identification and study of extinguished O+B+WR stars, the derivation of their extinction characteristics, and the cataloguing of F and G stars in the solar neighbourhood. Its data will be also used for a variety of other stellar studies and to generate a high-resolution continuum-free map of the Hα emission in the Galactic plane. We describe the techniques and the pipeline that are being used to process the data, including the basis of an innovative calibration system based on Gaia DR2 and 2MASS photometry.
We cross-match the Alma catalog of OB stars with Gaia DR2 astrometry and photometry as a first step towards producing a clean sample of massive stars in the solar neighbourhood with a high degree of completeness. We analyze the resulting colour-absolute magnitude diagram to divide our sample into categories and compare extinction estimates from two sources, finding problems with both of them. The distances obtained with three different priors are found to have few differences among them, indicating that Gaia DR2 distances are robust. An analysis of the 3-D distribution of massive stars in the solar neighbourhood is presented. We show that a kinematically distinct structure we dub the Cepheus spur extends from the Orion-Cygnus spiral arm towards the Perseus arm and is located above the Galactic mid-plane, likely being related to the recently discovered Radcliffe wave. We propose that this corrugation pattern in the Galactic disk may be responsible for the recent enhanced star formation at its crests and troughs. We also discuss our plans to extend this work in the immediate future.
OB associations are unbound groups of young stars made prominent by their bright OB members, and have long been thought to be the expanded remnants of dense star clusters. They have been important in astrophysics for over a century thanks to their luminous massive stars, though their low-mass members have not been well studied until the last couple of decades. This has changed thanks to data from X-ray observations, spectroscopic surveys and astrometry from Gaia that allows their full stellar content to be identified and their dynamics to be studied, which in turn is leading to changes in our understanding of these systems and their origins, with the old picture of Blaauw (1964a) now being superseded. It is clear now that OB associations have considerably more substructure than once envisioned, both spatially, kinematically and temporally. These changes have implications for the star formation process, the formation and evolution of planetary systems, and the build-up of stellar populations across galaxies.
Context. The spectral classifications of the Galactic O-Star Spectroscopic Survey (GOSSS) and the astrometric and photometric data from Gaia have significantly improved our ability to measure distances and determine memberships of stellar groups (clusters, associations, or parts thereof) with OB stars. In the near future, the situation will be further improved thanks to subsequent Gaia data releases and new photometric and spectroscopic surveys.
Aims. We initiated a program to identify and determine the membership of Galactic stellar groups with OB stars and measure distances to them. Given the data currently available, we started with the identification and distance determinations of groups with O stars. In this paper, we concentrate on groups that contain stars with the earliest spectral subtypes.
Methods. We used GOSSS to select Galactic stellar groups with O2–O3.5 stars and the method described in paper 0 of this series, which combines Gaia DR2 G + G BP + G RP photometry, positions, proper motions, and parallaxes to assign robust memberships and measure distances. We also included Collinder 419 and NGC 2264, the clusters cited in that paper, to generate our first list of 16 O-type Galactic stellar groups.
Results. We derived distances, determined the membership, and analyzed the structure of sixteen Galactic stellar groups with O stars, Villafranca O-001 to Villafranca O-016, including the fourteen groups with the earliest-O-type optically accessible stars known in the Milky Way. We compared our distance with previous results from the literature and establish that the best consistency is with (the small number of) VLBI parallaxes and the worst is with kinematic distances. Our results indicate that very massive stars can form in relatively low-mass clusters or even in near-isolation, as is the case for the Bajamar star in the North America nebula. This lends support to the hierarchical scenario of star formation, where some stars are born in well-defined bound clusters but others are born in associations that are unbound from the beginning: groups of newborn stars come in many shapes and sizes. We propose that HD 64 568 and HD 64 315 AB could have been ejected simultaneously from Haffner 18 (Villafranca O-012 S). Our results are consistent with a difference of ≈20 μ as in the Gaia DR2 parallax zero point between bright and faint stars.
We have detected a broad interstellar absorption band centred close to 7700 Å and with a FWHM of 176.6±3.9 Å. This is the first such absorption band detected in the optical range and is significantly wider than the numerous diffuse interstellar bands (DIBs). It remained undiscovered until now because it is partially hidden behind the A telluric band produced by O2. The band was discovered using STIS@HST spectra and later detected in a large sample of stars of diverse type (OB stars, BA supergiants, red giants) using further STIS and ground-based spectroscopy. The EW of the band is measured and compared with our extinction and K i λλ7667.021,7701.093 measurements for the same sample. The carrier is ubiquitous in the diffuse and translucent Galactic ISM but is depleted in the environment around OB stars. In particular, it appears to be absent or nearly so in sightlines rich in molecular carbon. This behaviour is similar to that of the σ-type DIBs, which originate in the low/intermediate-density UV-exposed ISM but are depleted in the high-density UV-shielded molecular clouds. We also present an update on our previous work on the relationship between E(4405 − 5495) and R5495 and incorporate our results into a general model of the ISM.
In this paper, we analyse how to extract the physical properties from the GALANTE photometry of a stellar sample. We propose a direct comparison between the observational colours (photometric bands normalized to the 515 nm central wavelength) and the synthetic colours derived from different stellar libraries. We use the reduced χ2 as the figure of merit for selecting the best fitting between both colour sets. The synthetic colours of the Next Generation Spectral Library (NGSL) provide a valuable sample for testing the uncertainty and precision of the stellar parameters derived from observational data. Reddening, as an extrinsic stellar physical parameter becomes a crucial variable for accounting for the errors and bias in the derived estimates: the higher the reddenings, the larger the errors and uncertainties in the derived parameters. NGSL colours also enable us to compare different theoretical stellar libraries for the same set of physical parameters, where we see how different catalogues of models can provide very different solutions in a, sometimes, non-linear way. This peculiar behaviour makes us to be cautious with the derived physical parameters obtained from GALANTE photometry without previous detailed knowledge of the theoretical libraries used to this end. In addition, we carry out the experiment of deriving physical stellar parameters from some theoretical libraries, using some other libraries as observational data. In particular, we use the Kurucz and Coelho libraries, as input observational data, to derive stellar parameters from Coelho + TLUSTY and Kurucz + TLUSTY stellar libraries, respectively, for different photometric errors and colour excesses.
