Reddening-free Q indices to identify Be star candidates
Yael Aidelman, Carlos Escudero, Franco Ronchetti, Facundo Quiroga, Laura Lanzarini
备注：
14 pages, 4 figures, Accepted for inclusion in the JCC-BD&ET 2020 minutes book, which will be published in the Springer series CCIS - Communications in Computer and Information Science
Astronomical databases currently provide high-volume spectroscopic and photometric data. While spectroscopic data is better suited to the analysis of many astronomical objects, photometric data is relatively easier to obtain due to shorter telescope usage time. Therefore, there is a growing need to use photometric information to automatically identify objects for further detailed studies, specially Hα emission line stars such as Be stars. Photometric color-color diagrams (CCDs) are commonly used to identify this kind of objects. However, their identification in CCDs is further complicated by the reddening effect caused by both the circumstellar and interstellar gas. This effect prevents the generalization of candidate identification systems. Therefore, in this work we evaluate the use of neural networks to identify Be star candidates from a set of OB-type stars. The networks are trained using a labeled subset of the VPHAS+ and 2MASS databases, with filters u, g, r, Hα, i, J, H, and K. In order to avoid the reddening effect, we propose and evaluate the use of reddening-free Q indices to enhance the generalization of the model to other databases and objects. To test the validity of the approach, we manually labeled a subset of the database, and use it to evaluate candidate identification models. We also labeled an independent dataset for cross dataset evaluation. We evaluate the recall of the models at a 99% precision level on both test sets. Our results show that the proposed features provide a significant improvement over the original filter magnitudes.
We are conducting a proper-motion survey for young brown dwarfs in the Taurus-Auriga molecular cloud based on the Pan-STARRS1 3$π$ Survey. Our search uses multi-band photometry and astrometry to select candidates, and is wider (370 deg$^{2}$) and deeper (down to $\approx$3 M$_{\rm Jup}$) than previous searches. We present here our search methods and spectroscopic follow-up of our high-priority candidates. Since extinction complicates spectral classification, we have developed a new approach using low-resolution ($R \approx 100$) near-infrared spectra to quantify reddening-free spectral types, …
We analyze {\sl Hubble Space Telescope} observations of nine Large Magellanic Cloud star clusters with ages of 1--2 Gyr to search for evolved counterparts of blue straggler stars. Near the red clump regions in the clusters' color--magnitude diagrams, we find branches of evolved stars that are much brighter than normal evolved stars. We examine the effects of photometric artifacts, differential reddening, and field contamination. We conclude that these bright evolved stars cannot be explained by any of these effects. Our statistical tests show that the contributions of photometric uncertainties…
We study five Luminous Blue Variable (LBV) candidates in the Andromeda galaxy and one more (MN112) in the Milky Way. We obtain the same-epoch near-infrared (NIR) and optical spectra on the 3.5-meter telescope at the Apache Point Observatory and on the 6-meter telescope of the SAO RAS. The candidates show typical LBV features in their spectra: broad and strong hydrogen lines, HeI, FeII, and [FeII] lines. We estimate the temperatures, reddening, radii and luminosities of the stars using their spectral energy distributions. Bolometric luminosities of the candidates are similar to those of known L…
The majority of brown dwarfs show some level of photometric or spectro-photometric variability in different wavelength ranges. This variability allow us to trace the 3D atmospheric structures of variable brown dwarfs and directly-imaged exoplanets with radiative-transfer models and mapping codes. Nevertheless, to date, we do not have an informed method to pre-select the brown dwarfs that might show a higher variability amplitude for a thorough variability study. In this work, we designed and tested near-infrared spectral indices to pre-select the most likely variable mid- and late-T dwarfs, wh…
A Large Sample of Am Candidates from LAMOST Data Release 1
我们提出了一个样本的金属线星（Am）的候选人从大天区多目标光纤光谱望远镜数据发布1（LAMOST DR 1）。根据Am星钙元素丰度不足而铁元素丰度过高的特点，提出了一种由低分辨光谱中Ca Ⅱ K线和铁线的线指数导出的经验分离曲线。3537 Am候选星是从30，000多颗恒星中选出的，这些恒星通过LAMOST管道和目视检查被分类为A型或早期F星。然后，我们对这个样本进行了一些分析，最后提供了一个列表，这些Am候选人与10个相关参数。与其它星表相比，从LAMOST DR 1中选出的Am候选星总体上要暗淡得多。显然，我们的列表是对已知明亮Am星表的重要补充，它为研究这类化学奇特的恒星提供了宝贵的材料。
Optically visible post-AGB/RGB stars and young stellar objects in the Small Magellanic Cloud: candidate selection, spectral energy distributions and spectroscopic examination
We have found three new LBV candidates in the star-forming galaxy NGC 4736. They show typical well-known LBV spectra, broad and strong hydrogen lines, He I lines, many Fe II lines, and forbidden [Fe II] and [Fe III]. Using archival Hubble Space Telescope and ground-based telescope data, we have estimated the bolometric magnitudes of these objects from -8.4 to -11.5, temperatures, and reddening. Source NGC 4736_1 (Mv = -10.2 +/- 0.1 mag) demonstrated variability between 2005 and 2018 as Delta V = 1.1 mag and Delta B = 0.82 mag, the object belongs to LBV stars. NGC 4736_2 (Mv < -8.6 mag) shows P…
In savvy pursuit of Local Group blue massive stars
金属丰度在大质量恒星演化中的重要作用以及多天体摄谱仪和10米级望远镜的结合，导致了对本星系群大质量恒星的大量系统研究。虽然基于颜色的蓝色大质量恒星的探索是相对成功的，但它们必须用光谱学来证实，并且通常导致以B型中等质量恒星为主的列表。我们已经开发了一个朋友的朋友代码来寻找本星系群中的OB协会，在Garcia et al.（2009）中提出。该方法的关键之一是从无红化Q参数中选择候选OB星的光度判据，该判据可以很容易地从GALEX扩展到近红外光度学。虽然不是一个新的想法，但我们的代码的强大优势之一是自动确定成员的进化质量，从而能够快速，更有见地地选择光谱学候选人，并识别潜在的高级进化阶段。我们介绍了我们在非常贫金属的不规则IC 1613上的工作（Garcia et al. 2010）。关联性质不仅是寻找最有趣的候选大质量恒星的有力帮助，而且还揭示了星系的结构和最近的恒星形成历史。
We present precise photometry and spectroscopy for 23 candidate spectrophotometric standard white dwarfs. The selected stars are distributed in the Northern hemisphere and around the celestial equators and are all fainter than r ~ 16.5 mag. This network of stars, when established as standards, together with the three Hubble Space Telescope primary CALSPEC white dwarfs, will provide a set of spectrophotometric standards to directly calibrate data products to better than 1%. These new faint standard white dwarfs will have enough signal-to-noise ratio in future deep photometric surveys and facili…
We study Luminous Blue Variable (LBV) candidate J004341.84+411112.0 in the Andromeda galaxy. We present optical spectra of the object obtained with the 6-m telescope of SAO RAS. The candidate shows typical LBV features in its spectra: broad and strong hydrogen lines and the He I lines with P Cigni profiles. Its remarkable spectral resemblance to the well known LBV P Cygni suggests a common nature of the objects and supports LBV classification of J004341.84+411112.0. We estimate the temperature, reddening, radius and luminosity of the star using its spectral energy distribution. Obtained bolome…
We combine LAMOST DR7 spectroscopic data and Gaia EDR3 photometric data to construct high-quality giant (0.7 $< (BP-RP) <$ 1.4) and dwarf (0.5 $< (BP-RP) < $ 1.5) samples in the high Galactic latitude region, with precise corrections for magnitude-dependent systematic errors in the Gaia photometry and careful reddening corrections using empirically determined color- and reddening-dependent coefficients. We use the two samples to build metallicity-dependent stellar loci of Gaia colors for giants and dwarfs, respectively. For a given $(BP-RP)$ color, a one dex change in [Fe/H] results in about a…
We present the first extensive X-ray study of the North-America and Pelican star-forming region (NGC7000/IC5070), with the aim of finding and characterizing its young stellar population. X-ray data from Chandra (four pointings) and XMM-Newton (seven pointings) were reduced and source detection was performed on each image. We complement the X-ray data with optical and near-IR data from the IPHAS, UKIDSS, and 2MASS catalogs, and with other published optical and Spitzer IR data. More than 700 X-ray sources are detected, the majority of which have an optical/NIR counterpart. This allows to identif…
Based on an extensive spectral study of a photometrically confirmed sample of Mira variables, we find a relationship between relative Balmer emission-line strength and spectral temperature of O-rich Mira stars. The $F_{\rm Hδ}/F_{\rm Hγ}$ flux ratio increases from less than unity to five as stars cool down from M0 to M10, which is likely driven by increasing TiO absorption above the deepest shock-emitting regions. We also discuss the relationship between the equivalent widths of the Balmer emission lines and the photometric luminosity phase of our Mira sample stars. Using our 291 Mira spectra …
Testing Cluster Membership of Planetary Nebulae with High-Precision Proper Motions. II. HST Observations of PHR J1315-6555 in the Open Cluster AL 1 (ESO 96-SC04)
本研究利用哈勃空间望远镜高精度自行运动数据，证实了行星状星云 PHR J1315-6555 隶属于疏散星团 AL 1，并测得该星团距离约13 kpc、年龄约1.0 Gyr，推算出其前身星初始质量约为2.1太阳质量。
Given its relative proximity (~430 pc), compact size (< 20'), young age (~ 0.5 Myr) and rich number of young stellar objects, the Serpens-South star forming region is a promising site for studying young sub-stellar objects, yet the low-mass members of this region remain largely undiscovered. In this paper we report on a deep photometric survey using a custom 1.45 um filter (W-band), as well as standard J and H near-IR filters, in order to identify candidate low-mass young brown-dwarfs in the Serpens-South region. We constructed a reddening-insensitive index (Q) by combining J, H and W-band pho…
