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Register a new userMEGARA-GTC Stellar Spectral Library (II). MEGASTAR First Release
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Esperanza Carrasco Dr
Publication date
2020
fields
Physics
and research's language is
English
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MEGARA is an optical integral field and multiobject fibre based spectrograph for the 10.4m Gran Telescopio CANARIAS that offers medium to high spectral resolutions (FWHM) of R $simeq$ 6000, 12000, 20000. Commissioned at the telescope in 2017, it started operation as a common-user instrument in 2018. We are creating an instrument-oriented empirical spectral library from MEGARA-GTC stars observations, MEGASTAR, crucial for the correct interpretation of MEGARA data. This piece of work describes the content of the first release of MEGASTAR, formed by the spectra of 414 stars observed with R $simeq$ 20000 in the spectral intervals from 6420 to 6790 $r{A}$ and from 8370 to 8885 $r{A}$, and obtained with a continuum average signal to noise ratio around 260. We describe the release sample, the observations, the data reduction procedure and the MEGASTAR database. Additionally, we include in Appendix A, an atlas with the complete set of 838 spectra of this first release of the MEGASTAR catalogue.
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MEGARA (Multi Espectr{o}grafo en GTC de Alta Resoluci{o}n para Astronom{i}a) is an optical (3650~--~9750AA), fibre-fed, medium-high spectral resolution (R = 6000, 12000, 20000) instrument for the GTC 10.4m telescope, commissioned in the summer of 2017, and currently in operation. The scientific exploitation of MEGARA demands a stellar-spectra library to interpret galaxy data and to estimate the contribution of the stellar populations. This paper introduces the MEGARA-GTC spectral library, detailing the rationale behind the catalogue building. We present the spectra of 97 stars (21 individual stars and 56 members of the globular cluster M15, being both sub-samples taken during the commissioning runs; and 20 stars from our on-going GTC Open-Time program). The spectra have R~=~20000 in the HR-R and HR-I setups, centred at 6563 and 8633~AA respectively. We describe the procedures to reduce and analyse the data. Then, we determine the best-fitting theoretical models to each spectrum through a $chi^{2}$ minimisation technique to derive the stellar physical parameters and discuss the results. We have also measured some absorption lines and indices. Finally, this article introduces our project to complete the library and the database to make the spectra available to the community.
We present the first release of the MaNGA Stellar Library (MaStar), which is a large, well-calibrated, high-quality empirical library covering the wavelength range of 3,622-10,354A at a resolving power of R~1800. The spectra were obtained using the same instrument as used by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) project, by piggybacking on the SDSS-IV/APOGEE-2N observations. Compared to previous empirical libraries, the MaStar library will have a higher number of stars and a more comprehensive stellar-parameter coverage, especially of cool dwarfs, low-metallicity stars, and stars with different [alpha/Fe], achieved by a sophisticated target selection strategy that takes advantage of stellar-parameter catalogs from the literature. This empirical library will provide a new basis for stellar population synthesis, and is particularly well-suited for stellar-population analysis of MaNGA galaxies. The first version of the library contains 8646 high-quality per-visit spectra for 3321 unique stars. Compared to photometry, the relative flux calibration of the library is accurate to 3.9% in g-r, 2.7% in r-i, and 2.2% in i-z. The data are released as part of Sloan Digital Sky Survey Data Release 15. We expect the final release of the library to contain more than 10,000 stars.
We present a comprehensive analysis of the compact planetary nebula M2-31 investigating its spectral properties, spatio-kinematical structure and chemical composition using GTC MEGARA integral field spectroscopic observations and NOT ALFOSC medium-resolution spectra and narrow-band images. The GTC MEGARA high-dispersion observations have remarkable tomographic capabilities, producing an unprecedented view of the morphology and kinematics of M2-31 that discloses a fast spectroscopic bipolar outflow along position angles 50$^circ$ and 230$^circ$, an extended shell and a toroidal structure or waist surrounding the central star perpendicularly aligned with the fast outflows. These observations also show that the C II emission is confined in the central region and enclosed by the [N II] emission. This is the first time that the spatial segregation revealed by a 2D map of the C II line implies the presence of multiple plasma components. The deep NOT ALFOSC observations allowed us to detect broad WR features from the central star of M2-31, including previously undetected broad O VI lines that suggest a reclassification as a [WO4]-type star.
We report the stellar atmospheric parameters for 7503 spectra contained in the first release of the MaNGA stellar library (MaStar) in SDSS DR15. The first release of MaStar contains 8646 spectra measured from 3321 unique stars, each covering the wavelength range 3622 AA to 10354 AA with a resolving power of $R sim$ 1800. In this work, we first determined the basic stellar parameters: effective temperature ($rm T_{eff}$), surface gravity ($log g$), and metallicity ($rm[Fe/H]$), which best fit the data using an empirical interpolator based on the Medium-resolution Isaac Newton Telescope library of empirical spectra (MILES), as implemented by the University of Lyon Spectroscopic analysis Software (Koleva et al. 2008, ULySS) package. While we analyzed all 8646 spectra from the first release of MaStar, since MaStar has a wider parameter-space coverage than MILES, not all of these fits are robust. In addition, not all parameter regions covered by MILES yield robust results, likely due to the non-uniform coverage of the parameter space by MILES. We tested the robustness of the method using the MILES spectra itself and identified a proxy based on the local density of the training set. With this proxy, we identified 7503 MaStar spectra with robust fitting results. They cover the range from 3179K to 20,517K in effective temperature ($rm T_{eff}$), from 0.40 to 5.0 in surface gravity ($log g$), and from $-$2.49 to $+$0.73 in metallicity ($rm[Fe/H]$).
We present a library of high-resolution (R $equiv$ $lambda$/$Delta$$lambda$ $sim$ 45,000) and high signal-to-noise ratio (S/N $geq$ 200) near-infrared spectra for stars of a wide range of spectral types and luminosity classes. The spectra were obtained with the Immersion GRating INfrared Spectrograph (IGRINS) covering the full range of the H (1.496-1.780 $mu$m) and K (2.080-2.460 $mu$m) atmospheric windows. The targets were primarily selected for being MK standard stars covering a wide range of effective temperatures and surface gravities with metallicities close to the Solar value. Currently, the library includes flux-calibrated and telluric-absorption-corrected spectra of 84 stars, with prospects for expansion to provide denser coverage of the parametric space. Throughout the H and K atmospheric windows, we identified spectral lines that are sensitive to $T_mathrm{eff}$ or $log g$ and defined corresponding spectral indices. We also provide their equivalent widths. For those indices, we derive empirical relations between the measured equivalent widths and the stellar atmospheric parameters. Therefore, the derived empirical equations can be used to calculate $T_mathrm{eff}$ and $log g$ of a star without requiring stellar atmospheric models.
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