Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Photometric Selection of M-dwarfs using Gaia, WISE and 2MASS photometry
106
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present criteria for the photometric selection of M-dwarfs using all-sky photometry, with a view to identifying M-dwarf candidates for inclusion in the input catalogues of upcoming all-sky surveys, including TESS and FunnelWeb. The criteria are based on Gaia, WISE and 2MASS all-sky photometry, and deliberately do not rely on astrometric information. In the lead-up to the availability of truly distance-limited samples following the release of Gaia DR2, this approach has the significant benefit of delivering a sample unbiased with regard to space velocity. Our criteria were developed by using Galaxia synthetic galaxy model predictions to evaluate both M-dwarf completeness and false-positive detections (i.e. non-M-dwarf contamination rates). In addition to the previously known sensitivity of J-H colour for giant-dwarf discrimination at cool temperatures, we find the WISE W1-W2 colour is also effective at discriminating M-dwarfs from cool giants. We have derived two sets of Gaia G > 14.5 criteria - a high-completeness set that contains 78,340 stars, of which 30.7-44.4% are expected to be M-dwarfs and contains 99.3% of the total number of expected M-dwarfs; and a low-contamination set that prioritises the stars most likely to be M-dwarfs at a cost of a reduction in completeness. This subset contains 40,505 stars and is expected to be comprised of 58.7-64.1% M-dwarfs, with a completeness of 98%. Comparison of the high-completeness set with the TESS Input Catalogue has identified 234 stars not currently in that catalogue, which preliminary analysis suggests could be useful M-dwarf targets for TESS. We also compared the criteria to selection via absolute magnitude and a combination of both methods. We found that colour selection in combination with an absolute magnitude limit provides the most effective way of selecting M-dwarfs en masse.
rate research
Read More
CONTEXT. 2MASS is the reference survey in the NIR part of the spectrum given its whole-sky coverage, large dynamic range, and proven calibration uniformity. However, previous studies disagree in the value of the zero points (ZPs) for its three bands JHK at the hundredth of a magnitude level. The disagreement should become more noticeable now that Gaia provides whole-sky optical photometry calibrated below that level. AIMS. We want to establish the value of the 2MASS ZPs based on NICMOS/HST spectrophotometry of the CALSPEC standard stars and test it with the help of Gaia DR2 parallaxes. METHODS. We have computed the synthetic JHK photometry for a sample of stars using the HST CALSPEC spectroscopic standards and compared it with their 2MASS magnitudes to evaluate the ZPs. We have tested our results by analysing a sample of FGK dwarfs with excellent 2MASS photometry and accurate Gaia DR2 parallaxes.} RESULTS. The Vega ZPs for 2MASS J, H, and K are found to be -0.025$pm$0.005 mag, 0.004$pm$0.005 mag, and -0.015$pm$0.005 mag, respectively. The analysis of the FGK sample indicates that the new ZPs are more accurate than previous ones.
CONTEXT: The second Gaia data release (DR2) took place on April 2018. DR2 included photometry for more than 1.3 10^9 sources in G, BP, and RP. Even though Gaia DR2 photometry is very precise, there are currently three alternative definitions of the sensitivity curves that show significative differences. AIMS: The aim of this paper is to improve the quality of the input calibration data to produce new compatible definitions of the three bands and to identify the reasons for the discrepancies between previous definitions. METHODS: We have searched the HST archive for STIS spectra with G430L+G750L data obtained with wide apertures and combined them with the CALSPEC library to produce a high quality SED library of 122 stars with a broad range of colors, including three very red stars. We have used it to compute new sensitivity curves for G, BP, and RP using a functional analytical formalism. RESULTS: The new curves are significantly better than the two previous attempts, REV and WEI. For G we confirm the existence of a systematic bias in magnitude and correct a color term present in REV. For BP we confirm the need to define two magnitude ranges with different sensitivity curves and measure the cut between them at G = 10.87 with a significant increase in precision. The new curves also fit the data better than either REV or WEI. For RP we obtain a sensitivity curve that better fits the STIS spectra and we find that the differences with previous attempts reside in a systematic effect between ground-based and HST spectral libraries. Additional evidence from color-color diagrams indicate that the new sensitivity curve is more accurate. Nevertheless, there is still room for improvement in the accuracy of the sensitivity curves because of the current dearth of good-quality red calibrators: adding more to the sample should be a priority before Gaia data release 3 takes place.
A precise interstellar dust extinction law is critically important to interpret observations. There are two indicators of extinction: the color excess ratio (CER) and the relative extinction. Compared to the CER, the wavelength-dependent relative extinction is more challenging to be determined. In this work, we combine spectroscopic, astrometric, and photometric data to derive high-precision CERs and relative extinction from optical to mid-infrared (IR) bands. A group of 61,111 red clump (RC) stars are selected as tracers by stellar parameters from APOGEE survey. The multiband photometric data are collected from Gaia, APASS, SDSS, Pan-STARRS1, 2MASS, and WISE surveys. For the first time, we calibrate the curvature of CERs in determining CERs E(lambda-GRP)/E(GBP-GRP) from color excess--color excess diagrams. Through elaborate uncertainty analysis, we conclude that the precision of our CERs is significantly improved (sigma < 0.015). With parallaxes from Gaia DR2, we calculate the relative extinction A_GBP/A_GRP for 5051 RC stars. By combining the CERs with the A_GBP/A_GRP, the optical--mid-IR extinction A_lambda/A_GRP has been determined in a total of 21 bands. Given no bias toward any specific environment, our extinction law represents the average extinction law with the total-to-selective extinction ratio Rv=3.16+-0.15. Our observed extinction law supports an adjustment in parameters of the CCM Rv=3.1 curve, together with the near-IR power-law index alpha=2.07+-0.03. The relative extinction values of HST and JWST near-IR bandpasses are predicted in 2.5% precision. As the observed reddening/extinction tracks are curved, the curvature correction needs to be considered when applying extinction correction.
We explored the AllWISE catalogue of the Wide-field Infrared Survey Explorer mission and identified Young Stellar Object candidates. Reliable 2MASS and WISE photometric data combined with Planck dust opacity values were used to build our dataset and to find the best classification scheme. A sophisticated statistical method, the Support Vector Machine (SVM) is used to analyse the multi-dimensional data space and to remove source types identified as contaminants (extragalactic sources, main sequence stars, evolved stars and sources related to the interstellar medium). Objects listed in the SIMBAD database are used to identify the already known sources and to train our method. A new all-sky selection of 133,980 Class I/II YSO candidates is presented. The estimated contamination was found to be well below 1% based on comparison with our SIMBAD training set. We also compare our results to that of existing methods and catalogues. The SVM selection process successfully identified >90% of the Class I/II YSOs based on comparison with photometric and spectroscopic YSO catalogues. Our conclusion is that by using the SVM, our classification is able to identify more known YSOs of the training sample than other methods based on colour-colour and magnitude-colour selection. The distribution of the YSO candidates well correlates with that of the Planck Galactic Cold Clumps in the Taurus--Auriga--Perseus--California region.
Aims: We explore the wealth of high quality photometric data provided by data release 2 of the Gaia mission for long period variables (LPVs) in the Large Magellanic Cloud. Our goal is to identify stars of various types and masses along the Asymptotic Giant Branch. Methods: For this endeavour, we developed a new multi-band approach combining Wesenheit functions W_{RP,BP-RP} and W_{K_s,J-K_s} in the Gaia BP, RP and 2MASS J, K_s spectral ranges, respectively, and use a new diagram (W_{RP,BP-RP}-W_{K_s,J-K_s}) versus K_s to distinguish between different kinds of stars in our sample of LPVs. We used stellar population synthesis models to validate our approach. Results:We demonstrate the ability of the new diagram to discriminate between O-rich and C-rich objects, and to identify low-mass, intermediate-mass and massive O-rich red giants, as well as extreme C-rich stars. Stellar evolution and population synthesis models guide the interpretation of the results, highlighting the diagnostic power of the new tool to discriminate between stellar initial masses, chemical properties and evolutionary stages.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
