Isolated star-forming regions containing Herbig Ae/Be stars. 1: The young stellar aggregate associated with BD +40deg 4124

Abstract In order to tackle the problems of low-mass end of the initial mass function (IMF) in star-forming regions and the formation mechanisms of brown dwarfs, we have conducted deep infrared surveys of nearby molecular clouds. We have found a significant population of very low-luminosity sources with IR excesses in the Taurus cloud and the Chamaeleon cloud core regions whose extinction corrected J magnitudes are 3 to 8 mag fainter than those of typical T Tauri stars in the same cloud. Some of them are associated with even fainter companions. Follow-up IR spectroscopy has confirmed for the selected sources that their photospheric temperature is around 2000 to 3000 K. Thus, these very low-luminosity young stellar sources are most likely very low-mass T Tauri stars, and some of them might even be young brown dwarfs.

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Double trouble: Gaia reveals (proto)planetary systems that may experience more than one dense star-forming environment

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa182 ◽

2020 ◽

Vol 501 (1) ◽

pp. L12-L17

Author(s):

Christina Schoettler ◽

Richard J Parker

Keyword(s):

Planetary Systems ◽

Young Star ◽

Young Stars ◽

Orion Nebula ◽

External Effects ◽

Star Forming ◽

Star Forming Regions ◽

Ejection Process ◽

Runaway Stars

ABSTRACT Planetary systems appear to form contemporaneously around young stars within young star-forming regions. Within these environments, the chances of survival, as well as the long-term evolution of these systems, are influenced by factors such as dynamical interactions with other stars and photoevaporation from massive stars. These interactions can also cause young stars to be ejected from their birth regions and become runaways. We present examples of such runaway stars in the vicinity of the Orion Nebula Cluster (ONC) found in Gaia DR2 data that have retained their discs during the ejection process. Once set on their path, these runaways usually do not encounter any other dense regions that could endanger the survival of their discs or young planetary systems. However, we show that it is possible for star–disc systems, presumably ejected from one dense star-forming region, to encounter a second dense region, in our case the ONC. While the interactions of the ejected star–disc systems in the second region are unlikely to be the same as in their birth region, a second encounter will increase the risk to the disc or planetary system from malign external effects.

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Giant Molecular Cloud Formation at the Interface of Colliding Supershells in the Large Magellanic Cloud

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab1202 ◽

2021 ◽

Author(s):

Kosuke Fujii ◽

Norikazu Mizuno ◽

J R Dawson ◽

Tsuyoshi Inoue ◽

Kazufumi Torii ◽

...

Keyword(s):

Large Magellanic Cloud ◽

Cloud Formation ◽

Beam Size ◽

Star Forming ◽

Star Forming Regions ◽

Long Baseline ◽

Gravitational Instabilities ◽

Atomic Medium ◽

High Column ◽

Compact Array

Abstract We investigate the H i envelope of the young, massive GMCs in the star-forming regions N48 and N49, which are located within the high column density H i ridge between two kpc-scale supergiant shells, LMC 4 and LMC 5. New long-baseline H i 21 cm line observations with the Australia Telescope Compact Array (ATCA) were combined with archival shorter baseline data and single dish data from the Parkes telescope, for a final synthesized beam size of 24.75″ by 20.48″, which corresponds to a spatial resolution of ∼ 6 pc in the LMC. It is newly revealed that the H i gas is highly filamentary, and that the molecular clumps are distributed along filamentary H i features. In total 39 filamentary features are identified and their typical width is ∼ 21 (8–49) [pc]. We propose a scenario in which the GMCs were formed via gravitational instabilities in atomic gas which was initially accumulated by the two shells and then further compressed by their collision. This suggests that GMC formation involves the filamentary nature of the atomic medium.

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Multiwavelength analysis of OH Megamaser galaxies: The case of IRAS11506-3851

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320004317 ◽

2020 ◽

Vol 15 (S359) ◽

pp. 347-349

Author(s):

Carpes P. Hekatelyne ◽

Thaisa Storchi-Bergmann

Keyword(s):

Active Galactic Nuclei ◽

Hubble Space Telescope ◽

Galactic Nuclei ◽

Large Array ◽

Very Large Array ◽

Star Forming ◽

Star Forming Regions ◽

Field Unit ◽

Mixed Transition ◽

Integral Field

AbstractWe present Multi-Object Spectrograph (GMOS) Integral Field Unit (IFU), Hubble Space Telescope (HST) and Very Large Array (VLA) observations of the inner kpc of the OH Megamaser galaxy IRAS 11506-3851. In this work we discuss the kinematics and excitation of the gas as well as its radio emission. The HST images reveal an isolated spiral galaxy and the combination with the GMOS-IFU flux distributions allowed us to identify a partial ring of star-forming regions surrounding the nucleus with a radius of ≍500 pc. The emission-line ratios and excitation map reveal that the region inside the ring present mixed/transition excitation between those of Starbursts and Active Galactic Nuclei (AGN), while regions along the ring are excited by Starbursts. We suggest that we are probing a buried or fading AGN that could be both exciting the gas and originating an outflow.

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Hα emission-line stars in molecular clouds

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731578 ◽

2019 ◽

Vol 630 ◽

pp. A90 ◽

Cited By ~ 2

Author(s):

Bertil Pettersson ◽

Bo Reipurth

Keyword(s):

Molecular Clouds ◽

Young Stellar Objects ◽

Be Stars ◽

Stellar Objects ◽

Strong Concentration ◽

Ob Stars ◽

Star Forming ◽

Hα Emission ◽

Objective Prism ◽

Emission Stars

A deep objective-prism survey for Hα emission stars towards the Canis Major star-forming clouds was performed. A total of 398 Hα emitters were detected, 353 of which are new detections. There is a strong concentration of these Hα emitters towards the molecular clouds surrounding the CMa OB1 association, and it is likely that these stars are young stellar objects recently born in the clouds. An additional population of Hα emitters is scattered all across the region, and probably includes unrelated foreground dMe stars and background Be stars. About 90% of the Hα emitters are detected by WISE, of which 75% was detected with usable photometry. When plotted in a WISE colour–colour diagram it appears that the majority are Class II YSOs. Coordinates and finding charts are provided for all the new stars, and coordinates for all the detections. We searched the Gaia-DR2 catalogue and from 334 Hα emission stars with useful parallaxes, we selected a subset of 98 stars that have parallax errors of less than 20% and nominal distances in the interval 1050 to 1350 pc that surrounds a strong peak at 1185 pc in the distance distribution. Similarly, Gaia distances were obtained for 51 OB-stars located towards Canis Major and selected with the same parallax errors as the Hα stars. We find a median distance for the OB stars of 1182 pc, in excellent correspondence with the distance from the Hα stars. Two known runaway stars are confirmed as members of the association. Finally, two new Herbig-Haro objects are identified.

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