scholarly journals Variable stars in the Sh 2-170 H ii region

2020 ◽  
Vol 493 (1) ◽  
pp. 267-287
Author(s):  
Tirthendu Sinha ◽  
Saurabh Sharma ◽  
A K Pandey ◽  
R K Yadav ◽  
K Ogura ◽  
...  
Keyword(s):  
Main Sequence ◽  
Variable Mass ◽  
Variable Stars ◽  
T Tauri Stars ◽  
Class Iii ◽  
Star Forming ◽  
T Tauri ◽  
Locking Mechanism ◽  
Photometric Monitoring ◽  
Pms Stars

ABSTRACT We present multi-epoch deep (∼20 mag) Ic-band photometric monitoring of the Sh 2-170 star-forming region to understand the variability properties of pre-main-sequence (PMS) stars. We report identification of 47 periodic and 24 non-periodic variable stars with periods and amplitudes ranging from ∼4 h to 18 d and from ∼0.1 to 2.0 mag, respectively. We have further classified 49 variables as PMS stars (17 Class ii and 32 Class iii) and 17 as main-sequence (MS)/field star variables. A larger fraction of MS/field variables (88 per cent) show periodic variability as compared to the PMS variables (59 per cent). The ages and masses of the PMS variable stars are found to be comparable with those of T-Tauri stars. Their variability amplitudes show an increasing trend with the near-IR/mid-IR excess. The period distribution of the PMS variables shows two peaks, one near ∼1.5 d and the other near ∼4.5 d. It is found that the younger stars with thicker discs and envelopes seem to rotate slower than their older counterparts. These properties of the PMS variables support the disc-locking mechanism. Both the period and amplitude of PMS stars show decrease with increasing mass probably due to the effective dispersal of circumstellar discs in massive stars. Our results favour the notion that cool spots on weak line T-Tauri stars are responsible for most of their variations, while hot spots on classical T-Tauri stars resulting from variable mass accretion from an inner disc contribute to their larger amplitudes and irregular behaviours.

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 Magnetic fields of intermediate-mass T Tauri stars

2019 ◽  
Vol 622 ◽  
pp. A72 ◽  
Author(s):  
F. Villebrun ◽  
E. Alecian ◽  
G. Hussain ◽  
J. Bouvier ◽  
C. P. Folsom ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Large Population ◽  
T Tauri Stars ◽  
Magnetic Characteristics ◽  
Intermediate Mass ◽  
Surface Magnetic Field ◽  
T Tauri ◽  
Magnetic Stars ◽  
Pms Stars

Context. The origin of the fossil magnetic fields detected in 5 to 10% of intermediate-mass main sequence stars is still highly debated.Aims. We want to bring observational constraints to a large population of intermediate-mass pre-main sequence (PMS) stars in order to test the theory that convective-dynamo fields generated during the PMS phases of stellar evolution can occasionally relax into fossil fields on the main sequence.Methods. Using distance estimations, photometric measurements, and spectropolarimetric data from HARPSpol and ESPaDOnS of 38 intermediate-mass PMS stars, we determined fundamental stellar parameters (Teff,Landvsini) and measured surface magnetic field characteristics (including detection limits for non-detections, and longitudinal fields and basic topologies for positive detections). Using PMS evolutionary models, we determined the mass, radius, and internal structure of these stars. We compared different PMS models to check that our determinations were not model-dependant. We then compared the magnetic characteristics of our sample accounting for their stellar parameters and internal structures.Results. We detect magnetic fields in about half of our sample. About 90% of the magnetic stars have outer convective envelopes larger than ∼25% of the stellar radii, and heavier than ∼2% of the stellar mass. Going to higher mass, we find that the magnetic incidence in intermediate-mass stars drops very quickly, within a timescale on the order of few times 0.1 Myr. Finally, we propose that intermediate-mass T Tauri stars with large convective envelopes, close to the fully convective limit, have complex fields and that their dipole component strengths may decrease as the sizes of their convective envelopes decrease, similar to lower-mass T Tauri stars.

scholarly journals Optical photometric variable stars towards Cygnus OB7

2019 ◽  
Vol 487 (2) ◽  
pp. 1765-1776 ◽  
Author(s):  
Somnath Dutta ◽  
Soumen Mondal ◽  
Santosh Joshi ◽  
Ramkrishna Das
Keyword(s):  
Variable Stars ◽  
T Tauri Stars ◽  
Light Curves ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Rotation Rates ◽  
T Tauri ◽  
Photometric Observations ◽  
Sky Survey ◽  
Magnitude Diagram

ABSTRACT We present optical I-band light curves of the stars towards a star-forming region Cygnus OB7 from 17-night photometric observations. The light curves are generated from a total of 381 image frames with very good photometric precision. From the light curves of 1900 stars and their periodogram analyses, we detect 31 candidate variables including five previously identified. 14 out of 31 objects are periodic and exhibit the rotation rates in the range of 0.15–11.60 d. We characterize those candidate variables using optical/infrared colour–colour diagram and colour–magnitude diagram (CMD). From spectral indices of the candidate variables, it turns out that four are probably Classical T-Tauri stars (CTTSs), rest remain unclassified from present data, they are possibly field stars or discless pre-main-sequence stars towards the region. Based on their location on the various CMDs, the ages of two T Tauri Stars were estimated to be ∼5 Myr. The light curves indicate at least five of the periodic variables are eclipsing systems. The spatial distribution of young variable candidates on Planck 857 GHz (350 $\mu$m) and 2MASS (Two Micron All Sky Survey) Ks images suggest that at least two of the CTTSs are part of the active star-forming cloud Lynds 1003.

scholarly journals T Tauri Disk Lifetime in the Lupus Association

2015 ◽  
Vol 10 (S314) ◽  
pp. 191-192
Author(s):  
P. A. B. Galli ◽  
C. Bertout ◽  
R. Teixeira ◽  
C. Ducourant
Keyword(s):  
Main Sequence ◽  
T Tauri Stars ◽  
Young Stars ◽  
Main Sequence Stars ◽  
Disk Model ◽  
Star Forming ◽  
T Tauri

AbstractIn a recent study, we derived individual distances for a sample of pre-main sequence stars that define the comoving association of young stars in the Lupus star-forming region. Here, we use these new distances to investigate the mass and age distributions of Lupus T Tauri stars and derive the average disk lifetime in the Lupus association based on an empirical disk model.

scholarly journals The ASAS-SN catalogue of variable stars – VIII. ‘Dipper’ stars in the Lupus star-forming region

2020 ◽  
Vol 496 (3) ◽  
pp. 3257-3269 ◽  
Author(s):  
J W Bredall ◽  
B J Shappee ◽  
E Gaidos ◽  
T Jayasinghe ◽  
P Vallely ◽  
...  
Keyword(s):  
Main Sequence ◽  
Statistical Significance ◽  
Variable Stars ◽  
Young Stars ◽  
Light Curves ◽  
Young Stellar Objects ◽  
Circumstellar Dust ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri

ABSTRACT Some young stellar objects such as T Tauri-like ‘dipper’ stars vary due to transient partial occultation by circumstellar dust, and observations of this phenomenon inform us of conditions in the planet-forming zones close to these stars. Although many dipper stars have been identified with space missions such as Kepler/K2, ground-based telescopes offer longer term and multiwavelength perspectives. We identified 11 dipper stars in the Lupus star-forming region in data from the All-Sky Automated Survey for SuperNovae (ASAS-SN), and further characterized these using observations by the Las Cumbres Global Observatory Telescope (LCOGT) and the Transiting Exoplanet Survey Satellite (TESS), as well as archival data from other missions. Dipper stars were identified from a catalogue of nearby young stars and selected based on the statistical significance, asymmetry, and quasi-periodicity or aperiodicity of variability in their ASAS-SN light curves. All 11 stars lie above or redwards of the zero-age main sequence and have infrared (IR) excesses indicating the presence of full circumstellar discs. We obtain reddening–extinction relations for the variability of seven stars using our combined ASAS-SN-TESS and LCOGT photometry. In all cases, the slopes are below the ISM value, suggesting larger grains, and we find a tentative relation between the slope (grain size) and the $K_\text{s}-[22 \, \mu \text{m}]$ IR colour regarded as a proxy for disc evolutionary state.

scholarly journals Magnetic Activity of Pre-main Sequence Stars

2004 ◽  
Vol 219 ◽  
pp. 211-222
Author(s):  
Eric D. Feigelson
Keyword(s):  
Main Sequence ◽  
Magnetic Activity ◽  
T Tauri Stars ◽  
X Rays ◽  
Orion Nebula ◽  
Main Sequence Stars ◽  
Nearby Star ◽  
X Ray ◽  
T Tauri ◽  
Pms Stars

I review here recent advances in our understanding of magnetic activity in pre-main sequence (PMS) protostars and T Tauri stars. Results are based on recent imaging, spectroscopic and temporal studies of nearby star forming regions from the Chandra X — ray Observatory and XMM — Newton, including a first look at an ultradeep Chandra exposure of the Orion Nebula Cluster.Pre-main sequence stars exhibit a high level of X-ray emission dominated by a bewildering variety of magnetic reconnection flares. Activity is linked to bulk stellar properties — Lbol, mass, surface area or volume — rather than rotation. This suggests that dynamo processes in deeply convective PMS stars may fundamentally differ from the tachocline dynamo operating in main sequence stars.X-rays and MeV particles from magnetic flares will affect the circumstellar environment in PMS systems, particularly the protoplanetary disk. X-ray emission may influence: disk ionization, turbulence and viscosity; Jovian planet formation and migration; the production of meteoritic isotopes and melting of meteoritic chondrules; the heating and chemistry of the disk. X-ray surveys are also effective in locating post-T Tauri stars for disk evolution studies.

scholarly journals Magnetic Activity of T Tauri Stars

1992 ◽  
Vol 9 ◽  
pp. 653-654
Author(s):  
T. Montmerle
Keyword(s):  
Solar Activity ◽  
Main Sequence ◽  
Magnetic Activity ◽  
T Tauri Stars ◽  
X Rays ◽  
General Review ◽  
Near Ir ◽  
T Tauri ◽  
Low Mass ◽  
Pms Stars

T Tauri stars (TTS) are low-mass (M ≲ 1M⊙) pre-main sequence (PMS) stars (for a general review, see Bertout 1989). They have long been known to be variable from near-TIV to near-IR wavelengths, on timescales ranging from a few minutes to a few decades. They are observed to flare in many wavenlength rages, from X-rays to the radio, and all the existing evidence is consistent with a very strong magnetic activity, in many ways analogous to solar activity (for a review, see, e.g., Montmerle et al. 1991).

scholarly journals The role of magnetic fields in pre-main sequence stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 25-37 ◽  
Author(s):  
Gaitee A. J. Hussain ◽  
Evelyne Alecian
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Main Sequence ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Main Sequence Stars ◽  
T Tauri ◽  
First Results ◽  
Pms Stars

AbstractStrong, kilo-Gauss, magnetic fields are required to explain a range of observational properties in young, accreting pre-main sequence (PMS) systems. We review the techniques used to detect magnetic fields in PMS stars. Key results from a long running campaign aimed at characterising the large scale magnetic fields in accreting T Tauri stars are presented. Maps of surface magnetic flux in these systems can be used to build 3-D models exploring the role of magnetic fields and the efficiency with which magnetic fields can channel accretion from circumstellar disks on to young stars. Long-term variability in T Tauri star magnetic fields strongly point to a dynamo origin of the magnetic fields. Studies are underway to quantify how changes in magnetic fields affect their accretion properties. We also present the first results from a new programme that investigates the evolution of magnetic fields in intermediate mass (1.5–3M⊙) pre-main sequence stars as they evolve from being convective T Tauri stars to fully radiative Herbig AeBe stars.

The Infancy of Solar-Type Stars and its Relevance for the Origin of Life

1997 ◽  
Vol 161 ◽  
pp. 267-282 ◽  
Author(s):  
Thierry Montmerle
Keyword(s):  
Main Sequence ◽  
Solar Nebula ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Necessary Condition ◽  
Sequence Evolution ◽  
T Tauri ◽  
Solar Type ◽  
Optical Domain ◽  
The Origin Of Life

AbstractFor life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.

scholarly journals Very Low-Luminosity Objects in Star-Forming Regions

1998 ◽  
Vol 11 (1) ◽  
pp. 423-424
Author(s):  
Motohide Tamura ◽  
Yoichi Itoh ◽  
Yumiko Oasa ◽  
Alan Tokunaga ◽  
Koji Sugitani
Keyword(s):  
Brown Dwarfs ◽  
Mass Function ◽  
T Tauri Stars ◽  
Initial Mass Function ◽  
Formation Mechanisms ◽  
Star Forming ◽  
Star Forming Regions ◽  
T Tauri ◽  
Low Mass ◽  
Stellar Sources

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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