scholarly journals Hα emission-line stars in molecular clouds

2019 ◽  
Vol 630 ◽  
pp. A90 ◽  
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.

scholarly journals SK 1: A possible case of triggered star formation in perseus

2006 ◽  
Vol 2 (S237) ◽  
pp. 217-221
Author(s):  
Miriam Rengel ◽  
Klaus Hodapp ◽  
Jochen Eislöffel
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Thermal Emission ◽  
Young Stellar Objects ◽  
Wide Field ◽  
Dust Shell ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Suitable Target

AbstractAccording to a triggered star formation scenario (e.g. Martin-Pintado & Cernicharo 1987) outflows powered by young stellar objects shape the molecular clouds, can dig cavities, and trigger new star formation. NGC 1333 is an active site of low- and intermediate star formation in Perseus and is a suggested site of self-regulated star formation (Norman & Silk 1980). Therefore it is a suitable target for a study of triggered star formation (e.g. Sandell & Knee 2001, SK1). On the other hand, continuum sub-mm observations of star forming regions can detect dust thermal emission of embedded sources (which drive outflows), and further detailed structures.Within the framework of our wide-field mapping of star formation regions in the Perseus and Orion molecular clouds using SCUBA at 850 and 450 μm, we mapped NCG 1333 with an area of around 14′× 21′. The maps show more structure than the previous maps of the region observed in sub-mm. We have unveiled the known embedded SK 1 source (in the dust shell of the SSV 13 ridge) and detailed structure of the region, among some other young protostars.In agreement with the SK 1 observations, our map of the region shows lumpy filaments and shells/cavities that seem to be created by outflows. The measured mass of SK 1 (~0.07 M) is much less than its virial mass (~0.2-1 M). Our observations support the idea of SK 1 as an event triggered by outflow-driven shells in NGC 1333 (induced by an increase in gas pressure and density due to radiation pressure from the stellar winds that have presumably created the dust shell). This kind of evidences provides a more thorough understanding of the star formation regulation processes.

scholarly journals On the Mass Accretion Rates of Herbig Ae/Be Stars. Magnetospheric Accretion or Boundary Layer?

Galaxies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 39
Author(s):  
Ignacio Mendigutía
Keyword(s):  
Boundary Layer ◽  
Magnetic Fields ◽  
Young Stellar Objects ◽  
Driving Mechanism ◽  
Be Stars ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri ◽  
Accretion Rates ◽  
Magnetospheric Accretion

Understanding how young stars gain their masses through disk-to-star accretion is of paramount importance in astrophysics. It affects our knowledge about the early stellar evolution, the disk lifetime and dissipation processes, the way the planets form on the smallest scales, or the connection to macroscopic parameters characterizing star-forming regions on the largest ones, among others. In turn, mass accretion rate estimates depend on the accretion paradigm assumed. For low-mass T Tauri stars with strong magnetic fields there is consensus that magnetospheric accretion (MA) is the driving mechanism, but the transfer of mass in massive young stellar objects with weak or negligible magnetic fields probably occurs directly from the disk to the star through a hot boundary layer (BL). The intermediate-mass Herbig Ae/Be (HAeBe) stars bridge the gap between both previous regimes and are still optically visible during the pre-main sequence phase, thus constituting a unique opportunity to test a possible change of accretion mode from MA to BL. This review deals with our estimates of accretion rates in HAeBes, critically discussing the different accretion paradigms. It shows that although mounting evidence supports that MA may extend to late-type HAes but not to early-type HBes, there is not yet a consensus on the validity of this scenario versus the BL one. Based on MA and BL shock modeling, it is argued that the ultraviolet regime could significantly contribute in the future to discriminating between these competing accretion scenarios.

scholarly journals Planetesimals around stars with TESS (PAST) – I. Transient dimming of a binary solar analogue at the end of the planet accretion era

2019 ◽  
Vol 488 (4) ◽  
pp. 4465-4476 ◽  
Author(s):  
E Gaidos ◽  
T Jacobs ◽  
D LaCourse ◽  
A Vanderburg ◽  
S Rappaport ◽  
...  
Keyword(s):  
Planet Formation ◽  
Infrared Emission ◽  
Young Stellar Objects ◽  
Circumstellar Dust ◽  
Wide Field ◽  
Be Stars ◽  
Solar Mass ◽  
Lithium Abundance ◽  
Stellar Objects ◽  
Star Forming

ABSTRACT We report detection of quasi-periodic (1.5-d) dimming of HD 240779, the solar-mass primary in a 5 arcsec visual binary (also TIC 284730577), by the Transiting Exoplanet Survey Satellite. This dimming, as has been shown for other ‘dipper’ stars, is likely due to occultation by circumstellar dust. The barycentric space motion, lithium abundance, rotation, and chromospheric emission of the stars in this system point to an age of ≈125 Myr, and possible membership in the AB Doradus moving group. As such it occupies an important but poorly explored intermediate regime of stars with transient dimming between young stellar objects in star-forming regions and main-sequence stars, and between UX Orionis-type Ae/Be stars and M-type ‘dippers’. HD 240779, but not its companion BD+10 714B, has Wide-field Infrared Survey Explorer (WISE)-detected excess infrared emission at 12 and 22 μm indicative of circumstellar dust. We propose that infrared emission is produced by collisions of planetesimals during clearing of a residual disc at the end of rocky planet formation, and that quasi-periodic dimming is produced by the rapid disintegration of a ≳100 km planetesimal near the silicate evaporation radius. Further studies of this and similar systems will illuminate a poorly understood final phase of rocky planet formation like that which produced the inner Solar system.

scholarly journals Variability of young stellar objects in the star-forming region Pelican Nebula

2019 ◽  
Vol 627 ◽  
pp. A135 ◽  
Author(s):  
A. Bhardwaj ◽  
N. Panwar ◽  
G. J. Herczeg ◽  
W. P. Chen ◽  
H. P. Singh
Keyword(s):  
Main Sequence ◽  
T Tauri Stars ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Physical Parameters ◽  
Main Sequence Stars ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri ◽  
Optical Wavelengths

Context. Pre-main-sequence variability characteristics can be used to probe the physical processes leading to the formation and initial evolution of both stars and planets. Aims. The photometric variability of pre-main-sequence stars is studied at optical wavelengths to explore star–disk interactions, accretion, spots, and other physical mechanisms associated with young stellar objects. Methods. We observed a field of 16′ × 16′ in the star-forming region Pelican Nebula (IC 5070) at BVRI wavelengths for 90 nights spread over one year in 2012−2013. More than 250 epochs in the VRI bands are used to identify and classify variables up to V ∼ 21 mag. Their physical association with the cluster IC 5070 is established based on the parallaxes and proper motions from the Gaia second data release (DR2). Multiwavelength photometric data are used to estimate physical parameters based on the isochrone fitting and spectral energy distributions. Results. We present a catalog of optical time-series photometry with periods, mean magnitudes, and classifications for 95 variable stars including 67 pre-main-sequence variables towards star-forming region IC 5070. The pre-main-sequence variables are further classified as candidate classical T Tauri and weak-line T Tauri stars based on their light curve variations and the locations on the color-color and color-magnitude diagrams using optical and infrared data together with Gaia DR2 astrometry. Classical T Tauri stars display variability amplitudes up to three times the maximum fluctuation in disk-free weak-line T Tauri stars, which show strong periodic variations. Short-term variability is missed in our photometry within single nights. Several classical T Tauri stars display long-lasting (≥10 days) single or multiple fading and brightening events of up to two magnitudes at optical wavelengths. The typical mass and age of the pre-main-sequence variables from the isochrone fitting and spectral energy distributions are estimated to be ≤1 M⊙ and ∼2 Myr, respectively. We do not find any correlation between the optical amplitudes or periods with the physical parameters (mass and age) of pre-main-sequence stars. Conclusions. The low-mass pre-main-sequence stars in the Pelican Nebula region display distinct variability and color trends and nearly 30% of the variables exhibit strong periodic signatures attributed to cold spot modulations. In the case of accretion bursts and extinction events, the average amplitudes are larger than one magnitude at optical wavelengths. These optical magnitude fluctuations are stable on a timescale of one year.

scholarly journals Far-IR Spectrophotometry of HH Flows with the ISO Long-Wavelength Spectrometer

1997 ◽  
Vol 182 ◽  
pp. 111-120
Author(s):  
R. Liseau ◽  
T. Giannini ◽  
B. Nisini ◽  
P. Saraceno ◽  
L. Spinoglio ◽  
...  
Keyword(s):  
Mass Loss ◽  
Line Emission ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Shock Models ◽  
Ir Spectrophotometry ◽  
Hh Objects ◽  
Loss Rates

Full Iso-Lws spectral scans between about 45 to 190 μm of 17 individual HH objects in 7 star forming regions have revealed essentially only [O I] 63 μm line emission, implying that the Fircooling of these objects is totally dominated by this line alone. In this case, J-shock models can be used to determine the mass loss rates of the HH exciting sources. These mass loss rates are in reasonably good agreement with those estimated for the accompanying CO flows, providing first observational evidence that HH and molecular flows are driven by the same agent. The Lmech – Lbol relation, based on our results with the Lws, implies that young stellar objects of lower mass are loosing mass at relatively higher rates than their more massive counterparts.

scholarly journals Identification of Young Stellar Object candidates in the Gaia DR2 x AllWISE catalogue with machine learning methods

2019 ◽  
Vol 487 (2) ◽  
pp. 2522-2537 ◽  
Author(s):  
G Marton ◽  
P Ábrahám ◽  
E Szegedi-Elek ◽  
J Varga ◽  
M Kun ◽  
...  
Keyword(s):  
Machine Learning ◽  
3D Structure ◽  
Physical Nature ◽  
Machine Learning Techniques ◽  
Young Stellar Objects ◽  
Support Vector ◽  
Wide Field ◽  
Stellar Objects ◽  
Star Forming ◽  
Gaia Dr2

ABSTRACT The second Gaia Data Release (DR2) contains astrometric and photometric data for more than 1.6 billion objects with mean Gaia G magnitude <20.7, including many Young Stellar Objects (YSOs) in different evolutionary stages. In order to explore the YSO population of the Milky Way, we combined the Gaia DR2 data base with Wide-field Infrared Survey Explorer (WISE) and Planck measurements and made an all-sky probabilistic catalogue of YSOs using machine learning techniques, such as Support Vector Machines, Random Forests, or Neural Networks. Our input catalogue contains 103 million objects from the DR2xAllWISE cross-match table. We classified each object into four main classes: YSOs, extragalactic objects, main-sequence stars, and evolved stars. At a 90 per cent probability threshold, we identified 1 129 295 YSO candidates. To demonstrate the quality and potential of our YSO catalogue, here we present two applications of it. (1) We explore the 3D structure of the Orion A star-forming complex and show that the spatial distribution of the YSOs classified by our procedure is in agreement with recent results from the literature. (2) We use our catalogue to classify published Gaia Science Alerts. As Gaia measures the sources at multiple epochs, it can efficiently discover transient events, including sudden brightness changes of YSOs caused by dynamic processes of their circumstellar disc. However, in many cases the physical nature of the published alert sources are not known. A cross-check with our new catalogue shows that about 30 per cent more of the published Gaia alerts can most likely be attributed to YSO activity. The catalogue can be also useful to identify YSOs among future Gaia alerts.

scholarly journals Physical Properties of Molecular Envelopes in Low-Mass Star-Forming Regions

2000 ◽  
Vol 197 ◽  
pp. 61-70
Author(s):  
Nagayoshi Ohashi
Keyword(s):  
Physical Properties ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Narrow Line ◽  
Stellar Objects ◽  
Velocity Pattern ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Line Widths

We have carried out interferometric observations of pre-protostellar and protostellar envelopes in Taurus. Protostellar envelopes are dense gaseous condensations with young stellar objects or protostars, while pre-protostellar envelopes are those without any known young stellar objects. Five pre-protostellar envelopes have been observed in CCS JN=32–21, showing flattened and clumpy structures of the envelopes. The observed CCS spectra show moderately narrow line widths, ~0.1 to ~0.35 km s–1. One pre-protostellar envelope, L1544, shows a remarkable velocity pattern, which can be explained in terms of infall and rotation. Our C18O J=1–0 observations of 8 protostellar envelopes show that they have also flattened structures like pre-protostellar envelopes but no clumpy structures. Four out the eight envelopes show velocity patterns that can be explained by motions of infall (and rotation). Physical properties of pre-protostellar and protostellar envelopes are discussed in detail.

scholarly journals Bipolar Outflows and Stellar Jets

1987 ◽  
Vol 115 ◽  
pp. 213-237 ◽  
Author(s):  
Ronald L. Snell
Keyword(s):  
Physical Properties ◽  
High Velocity ◽  
Molecular Clouds ◽  
Early Stage ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Bipolar Outflows ◽  
Stellar Objects ◽  
Stellar Jets ◽  
Almost All

A wealth of data is now available on the energetic mass outflows that are associated with young stellar objects. This phenomenon is thought to occur at a very early stage in the evolution of stars of almost all masses. The discovery of this energetic event was first made through observations of the rapidly expanding molecular gas that surrounds many of these young stellar objects. A review of the physical properties, including the energetics and morphology, of the expanding molecular gas is presented in this paper. In addition, the role these energetic winds play in affecting the dynamics of the parental molecular clouds is also discussed. Finally, the results of detailed studies of the structure and kinematics of the high velocity molecular gas are reviewed and the evidence for existance of wind-swept cavities and molecular shells within the clouds are presented.

scholarly journals Abundant, hot water toward young stellar objects

1997 ◽  
Vol 178 ◽  
pp. 397-400
Author(s):  
F.P. Helmich ◽  
E.F. Van Dishoeck ◽  
J.H. Black ◽  
Th. De Graauw
Keyword(s):  
Hot Water ◽  
Resolving Power ◽  
Young Stellar Objects ◽  
Small Scale ◽  
Interstellar Space ◽  
Infrared Space Observatory ◽  
Direct Estimate ◽  
Infrared Source ◽  
Stellar Objects ◽  
Star Forming

The large amount of water vapour in the Earth's atmosphere makes it extremely difficult to observe water in interstellar space, except under unusual conditions (e.g., masers). The Short Wavelength Spectrometer (SWS; de Graauw et al. 1996) on board the Infrared Space Observatory (ISO) provides an unique opportunity to study the ro-vibrational fundamental bands of water in absorption against bright infrared continuum sources. Such absorption line data have several advantages over emission observations. For example, only a pencil beam to the infrared source is probed, which minimizes the complications due to the small-scale physical and chemical heterogeneity of star-forming regions. In addition, lines from all rotational levels are present within a vibrational band, so that the complete spectrum yields a direct estimate of the level populations and excitation temperature along the line of sight. Other molecules, such as CO, HCN and C2H2, can be observed with the same technique, leading to accurate relative abundances. The main limitation of the ISO-SWS grating is its low spectral resolving power, λ/Δ λ ≈ 1350 at 6 μm, since the lines are intrinsically much narrower. This limits the sensitivity, so that only high column densities can be detected, and complicates the interpretation because detectable lines are often saturated. The low spectral resolution also blends the lines, making it difficult to determine the equivalent widths unambiguously. The ISO-SWS is therefore particularly sensitive to molecules in warm gas with relatively large line widths (Δ V > 3 km s−1).

scholarly journals Continuum Wavelength Emission from Embedded, Young, and Massive Stellar Objects Beyond 1 μm

1990 ◽  
Vol 139 ◽  
pp. 113-114
Author(s):  
Thomas Henning ◽  
Werner Pfau
Keyword(s):  
Molecular Clouds ◽  
Dust Emission ◽  
Average Energy ◽  
Hii Regions ◽  
Point Sources ◽  
Color Temperature ◽  
Stellar Objects ◽  
Ob Stars ◽  
Infrared Background ◽  
Wavelength Emission

One of the components of the galactic infrared background (GIRB) radiation is emission by warm dust grains heated by OB stars embedded in molecular clouds. The main contributors are compact HII regions and comparatively radioquiet infrared (IR) point sources such as the Becklin-Neugebauer object. We present the average energy distribution between 1 and 1300 μm for a sample of BN-type objects. The average color temperature between 60 and 100 μm is ~40 K, which is very similar to the color temperature of the observed warm galactic dust emission (WGDE).

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