The CMa R1 star-forming region contains several compact clusters as well as many young early-B stars. It is associated with a well-known bright rimmed nebula, the nature of which is unclear (fossil HII region or supernova remnant). To help elucidate the nature of the nebula, our goal was to reconstruct the star-formation history of the CMa R1 region, including the previously unknown older, fainter low-mass stellar population, using X-rays. We analyzed images obtained with the ROSAT satellite, covering ~5 sq. deg. Complementary VRI photometry was performed with the Gemini South telescope. Colour-magnitude and colour-colour diagrams were used in conjunction with pre-main sequence evolutionary tracks to derive the masses and ages of the X-ray sources. The ROSAT images show two distinct clusters. One is associated with the known optical clusters near Z CMa, to which ~40 members are added. The other, which we name the "GU CMa" cluster, is new, and contains ~60 members. The ROSAT sources are young stars with masses down to M_star ~0.5 M_sun, and ages up to 10 Myr. The mass functions of the two clusters are similar, but the GU CMa cluster is older than the cluster around Z CMa by at least a few Myr. Also, the GU CMa cluster is away from any molecular cloud, implying that star formation must have ceased; on the contrary (as already known), star formation is very active in the Z CMa region.
The 2008-2009 outburst of the young binary system Z CMa unraveled by interferometry with high spectral resolution
Z CMa是一个年轻的双星系统，由一个Herbig主星和一个FU Ori伴星组成。这两个组成部分似乎都被活跃的吸积盘所包围，赫比格B 0还伴随着一个喷流。2008年11月，K.格兰金发现Z CMa爆发的幅度比过去25年中记录的任何光度变化都要大。为了研究爆发发生的最内部区域并了解其起源，我们于2009年12月在中等和高光谱分辨率模式下用ABER/VLTI观测了跨越Brγ发射线的两个二元分量。我们的观测结果表明，赫比格Be，负责增加的亮度，也产生了强大的Brγ发射，他们允许我们从不同的来源，通过定位在每个速度通过线的发射解开。考虑一个模型的开普勒磁盘单独未能再现不对称的光谱天体测量，这表明一个流出的主要贡献。
Imaging and spectroscopy of the knots, clumps, and extended arcs in the complex ejecta of VY CMa confirm a record of high mass loss events over the past few hundred years. HST/STIS spectroscopy of numerous small knots close to the star allow us to measure their radial velocities from the strong K I emission and determine their separate motions, spatial orientations, and time since ejecta. Their ages concentrate around 70, 120, 200 and 250 years ago. A K I emission knot only 50 mas from the star ejected as recently as 1985 -- 1995 may coincide with an H2O maser. Comparison with VY CMa's histori…
The relationship between young stellar clusters and respective parental molecular clouds is still an open issue: for instance, are the similarities between substructures of clouds and clusters just a coincidence? Or would they be the indication of a physical relationship? In order to address these issues, we have studied the CMa OB1/R1 region that shows evidence for a complex star formation history. We obtained molecular clouds mapping with the IRAM-30 metre telescope to reveal the physical conditions of an unexplored side of the CMa region aiming to compare the morphology of the clouds with t…
An exotic environment surrounds the young stellar groups associated with the Canis Major (CMa) OB1/R1 region, which probably was formed under feedback from at least three supernova events having occurred a few million years ago. We use astrometric data from the Gaia-DR2 to confirm the membership of the stars in CMa R1, based on proper motion and parallax, which revealed 514 new members and candidates. The mean age of 5 Myr estimated from the color-magnitude diagram characterizes the sources as likely pre-main sequence candidates. In total, a sample of 694 stars detected with the T80-South tele…
Red supergiant stars (RSGs, Minit = 10-40Msun) are known to eject large amounts of material, as much as half of their initial mass during this evolutionary phase. However, the processes powering the mass ejection in low- and intermediate-mass stars do not work for RSGs and the mechanism that drives the ejection remains unknown. Different mechanisms have been proposed as responsible for this mass ejection but so far little is known about the actual processes taking place in these objects. Here we present high angular resolution interferometric ALMA maps of VY CMa continuum and molecular emissio…
Canis Major OB1 (CMa OB1) is a Galactic stellar association with a very intriguing star-formation scenario. There are more than two dozen known star clusters in its line of sight, but it is not clear which ones are physically associated with CMa OB1. We use a clustering code that employs 5-dimensional data from the Gaia DR2 catalogue to identify physical groups and obtain their astrometric parameters and, in addition, we use two different isochrone-fitting methods to estimate the ages of these groups. We find 15 stellar groups with distances between 570 pc and 1650 pc, including 10 previously …
The past photometric history of the FU Ori-type young eruptive star 2MASS J06593158-0405277 = V960 Mon
已知的FU Ori-type年轻爆发恒星非常罕见（大约有十几个确认的物体），2 MASS J 06593158 -0405277在2014年爆发，可能是该家族的最新成员。所有成员国在其有记录的历史中只出现过一次这样的喷发，这一事件持续了几十年。为了测试2 MASS J 06593158 -0405277的FU Ori性质，我们通过测量其在1899-1989年时间间隔的哈佛感光板上的亮度来重建其光度历史。以前没有发现类似于2014年开始的大幅度喷发，就像真正的FU Ori-type物体一样。2 MASS J 06593158 -0405277在静止期的亮度中值为B=15.5，在1935-1950年的时间间隔内，其特征是变化很大（约1等振幅），这与后来时期的光度稳定性形成了鲜明对比。在1935-1950年期间的变化可以归因于2 MASS J 06593158 -0405277本身的一些T Tau活动，或者归因于同样年轻和较暗的恒星2 MASS J 06593168 -0405224，它位于北面5角秒，在哈佛照相底片的天体测量尺度上形成了一对未解析的恒星。
Close encounters between young stellar objects in star forming clusters are expected to dramatically perturb circumstellar disks. Such events are witnessed in numerical simulations of star formation, but few direct observations of ongoing encounters have been made. Here we report sub-0".1 resolution Atacama Large Millimeter Array (ALMA) and Jansky Very Large Array (JVLA) observations towards the million year old binary protostar Z CMa in dust continuum and molecular line emission. A point source ~4700 au from the binary has been discovered at both millimeter and centimeter wavelengths. It is l…
Re-visiting the Canis Major star-forming region with Gaia data release 3 data
Universidade Cidade de São Paulo（圣保罗城市大学）；Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo（圣保罗大学天文、地球物理与大气科学研究所）；Universidad Nacional de Educación a Distancia (UNED)（西班牙国立远程教育大学）；Université de Bordeaux（波尔多大学）；Institut universitaire de France (IUF)（法国高等教育研究院）
Young stellar associations hold a star formation record that can persist for millions of years, revealing the progression of star formation long after the dispersal of the natal cloud. To identify nearby young stellar populations that trace this progression, we have designed a comprehensive framework for the identification of young stars, and use it to identify $\sim$3$\times 10^4$ candidate young stars within a distance of 333 pc using Gaia DR2. Applying the HDBSCAN clustering algorithm to this sample, we identify 27 top-level groups, nearly half of which have little to no presence in previou…
