Optical photometric variable stars towards Cygnus OB7

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.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935418 ◽

2019 ◽

Vol 627 ◽

pp. A135 ◽

Cited By ~ 3

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.

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An unusual abundance of T Tauri stars? NIR study of the southern high-mass star-forming region RCW 34

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309991414 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 384-384

Author(s):

H. M. de Villiers ◽

D. J. Van der Walt

Keyword(s):

T Tauri Stars ◽

High Mass ◽

Mass Star ◽

Main Sequence Stars ◽

Infrared Excess ◽

Frame Size ◽

Star Forming ◽

T Tauri ◽

Point Correlation ◽

Stellar Masses

AbstractRCW 34 is a special star-forming region with a few stars showing an infrared excess, but seems as if it has an uncommon abundance in T Tauri stars. This possibility was confirmed by (i) clustering of classical T Tauri (CTT) stars in the two-color diagram, (ii) clustering of pre-main-sequence stars in the color–magnitude diagram, as well as (iii) the significant clustering at dimensions larger than the image-frame size, indicated by the second ‘bump’ in the two-point correlation analysis. A possible explanation for the above features could be the existence of an underlying wide CTT cluster with a smaller cluster centered around the massive star. The Ks-band luminosity function (α = 0.31) of RCW 34 shows that it is indeed a region of low stellar masses with an age of about of 1 Myr. Spectroscopic confirmation of such an underlying T Tauri cluster is necessary before any definite conclusions can be reached.

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T Tauri Disk Lifetime in the Lupus Association

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315006262 ◽

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.

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Simultaneous Spectroscopic and Photometric Observations of the YY Orionis Star S CrA

International Astronomical Union Colloquium ◽

10.1017/s0252921100069219 ◽

1977 ◽

Vol 42 ◽

pp. 88-91

Author(s):

R. Mundt ◽

B. Wolf

Keyword(s):

Variable Stars ◽

T Tauri Stars ◽

Preliminary Results ◽

Observational Material ◽

T Tauri ◽

Photometric Observations

AbstractThe YY Orionis stars are a subclass of the T Tauri stars which show in their spectra evidence for infailing envelopes. They are interpreted as protostars in the final stages of their hydrodynamical evolution (Walker 1972, Appenzeller and Wolf 1977, Wolf et al. 1977).To get more information about the behaviour of these highly variable stars simultaneous spectroscopic and photoelectric (UBV) observations have been carried out in July 1977 at the ESO observatory at La Silla. Such observations of YY Orionis stars have never been done before.The most frequently observed star during our run was the bright YY Orionis star S CrA. The observational material is still under evaluation and therefore only some preliminary results are presented here. A more extended description and discussion of the observations will be published elsewhere (Mundt and Wolf, 1977).

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1588 ◽

2020 ◽

Vol 496 (3) ◽

pp. 3257-3269 ◽

Cited By ~ 1

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.

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Variable stars in the Sh 2-170 H ii region

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa206 ◽

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.

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Very Low-Luminosity Objects in Star-Forming Regions

Highlights of Astronomy ◽

10.1017/s1539299600021626 ◽

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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SuperWASP variable stars: classifying light curves using citizen science

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab140 ◽

2021 ◽

Vol 502 (1) ◽

pp. 1299-1311

Author(s):

Heidi B Thiemann ◽

Andrew J Norton ◽

Hugh J Dickinson ◽

Adam McMaster ◽

Ulrich C Kolb

Keyword(s):

Variable Stars ◽

Eclipsing Binaries ◽

Light Curves ◽

Data Set ◽

Resultant Data ◽

Sky Survey ◽

Short Period ◽

Contact Binaries ◽

Analysis Of Results

ABSTRACT We present the first analysis of results from the SuperWASP variable stars Zooniverse project, which is aiming to classify 1.6 million phase-folded light curves of candidate stellar variables observed by the SuperWASP all sky survey with periods detected in the SuperWASP periodicity catalogue. The resultant data set currently contains >1 million classifications corresponding to >500 000 object–period combinations, provided by citizen–scientist volunteers. Volunteer-classified light curves have ∼89 per cent accuracy for detached and semidetached eclipsing binaries, but only ∼9 per cent accuracy for rotationally modulated variables, based on known objects. We demonstrate that this Zooniverse project will be valuable for both population studies of individual variable types and the identification of stellar variables for follow-up. We present preliminary findings on various unique and extreme variables in this analysis, including long-period contact binaries and binaries near the short-period cut-off, and we identify 301 previously unknown binaries and pulsators. We are now in the process of developing a web portal to enable other researchers to access the outputs of the SuperWASP variable stars project.

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