Formation of star clusters with extended main-sequence turn-offs in the Magellanic Clouds: the origin of young stellar objects in older clusters

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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HII regions and young star clusters in the Magellanic Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900200387 ◽

1991 ◽

Vol 148 ◽

pp. 207-208

Author(s):

Myung Gyoon Lee

Keyword(s):

Main Sequence ◽

Star Clusters ◽

Hii Regions ◽

Young Star ◽

Magellanic Clouds ◽

Stellar Content ◽

Ccd Photometry ◽

Luminosity Functions ◽

Young Star Clusters ◽

Mass Functions

Using U BV CCD photometry, the stellar content of HII regions and young star clusters in the Magellanic Clouds has been studied: (1) the reddenings have been determined, and ages of OB associations and young star clusters have been measured; (2) the stellar initial mass functions have been determined by using the main-sequence luminosity functions; and (3) U BV CCD surface photometry of nine young star clusters has been obtained and their structural properties investigated.

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Oscillations in Young Stellar Objects

International Astronomical Union Colloquium ◽

10.1017/s0252921100016493 ◽

2002 ◽

Vol 185 ◽

pp. 352-353

Author(s):

F.J.G. Pinheiro ◽

D.F.M. Folha ◽

M.J.P.F.G. Monteiro ◽

M. Marconi ◽

V. Ripepi ◽

...

Keyword(s):

Light Curve ◽

Main Sequence ◽

Young Stellar Objects ◽

Stellar Objects ◽

Stellar Oscillations ◽

Pms Stars

AbstractWe report the discovery of periodicities in the light curve of the Herbig Ae star V346 Ori. We interpret these variations as the superposition of at least two signals with periods P1=42±6 min and P2=68±12 min resulting from stellar oscillations. The computation of linear non-adiabatic pulsation models for Pre-Main Sequence (PMS) stars reproduces these periods for a 1.5 M⊙ star with Teff= 7300 K and log L/L⊙= 0.74, pulsating in the fundamental and second overtones.

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The multiple young stellar objects of HBC 515: An X-ray and millimeter-wave imaging study in (pre-main sequence) diversity

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629545 ◽

2017 ◽

Vol 598 ◽

pp. A8

Author(s):

D. A. Principe ◽

G. G. Sacco ◽

J. H. Kastner ◽

D. Wilner ◽

B. Stelzer ◽

...

Keyword(s):

Millimeter Wave ◽

Main Sequence ◽

Imaging Study ◽

Sequence Diversity ◽

Young Stellar Objects ◽

Stellar Objects ◽

X Ray ◽

Millimeter Wave Imaging ◽

Wave Imaging

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OCAAT: automated analysis of star cluster colour-magnitude diagrams for gauging the local distance scale

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314011077 ◽

2014 ◽

Vol 10 (S306) ◽

pp. 298-300

Author(s):

Gabriel I. Perren ◽

Ruben A. Vázquez ◽

Andrés E. Piatti ◽

André Moitinho

Keyword(s):

Main Sequence ◽

Star Clusters ◽

Automated Analysis ◽

Star Cluster ◽

Magellanic Clouds ◽

Distance Scale ◽

Analysis Tool ◽

Large Set ◽

Uncertainty Estimates ◽

Local Distance

AbstractStar clusters are among the fundamental astrophysical objects used in setting the local distance scale. Despite its crucial importance, the accurate determination of the distances to the Magellanic Clouds (SMC/LMC) remains a fuzzy step in the cosmological distance ladder. The exquisite astrometry of the recently launched ESA Gaia mission is expected to deliver extremely accurate statistical parallaxes, and thus distances, to the SMC/LMC. However, an independent SMC/LMC distance determination via main sequence fitting of star clusters provides an important validation check point for the Gaia distances. This has been a valuable lesson learnt from the famous Hipparcos Pleiades distance discrepancy problem. Current observations will allow hundreds of LMC/SMC clusters to be analyzed in this light.Today, the most common approach for star cluster main sequence fitting is still by eye. The process is intrinsically subjective and affected by large uncertainties, especially when applied to poorly populated clusters. It is also, clearly, not an efficient route for addressing the analysis of hundreds, or thousands, of star clusters. These concerns, together with a new attitude towards advanced statistical techniques in astronomy and the availability of powerful computers, have led to the emergence of software packages designed for analyzing star cluster photometry. With a few rare exceptions, those packages are not publicly available.Here we present OCAAT (Open Cluster Automated Analysis Tool), a suite of publicly available open source tools that fully automatises cluster isochrone fitting. The code will be applied to a large set of hundreds of open clusters observed in the Washington system, located in the Milky Way and the Magellanic Clouds. This will allow us to generate an objective and homogeneous catalog of distances up to ~ 60 kpc along with its associated reddening, ages and metallicities and uncertainty estimates.

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Validating post-AGB candidates in the LMC and SMC using SALT spectra

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935392 ◽

2020 ◽

Vol 641 ◽

pp. A142

Author(s):

R. Szczerba ◽

M. Hajduk ◽

Ya. V. Pavlenko ◽

B. J. Hrivnak ◽

B. M. Kaminsky ◽

...

Keyword(s):

South African ◽

Stellar Atmosphere ◽

Magellanic Clouds ◽

Emission Lines ◽

Young Stellar Objects ◽

Agb Stars ◽

Large Telescope ◽

Stellar Objects ◽

Effective Temperatures ◽

The Continuum

We selected a sample of post-AGB candidates in the Magellanic Clouds on the basis of their near- and mid-infrared colour characteristics. Fifteen of the most optically bright post-AGB candidates were observed with the South African Large Telescope in order to determine their stellar parameters and thus to validate or discriminate their nature as post-AGB objects in the Magellanic Clouds. The spectral types of absorption-line objects were estimated according to the MK classification, and effective temperatures were obtained by means of stellar atmosphere modelling. Emission-line objects were classified on the basis of the fluxes of the emission lines and the presence of the continuum. Out of 15 observed objects, only 4 appear to be genuine post-AGB stars (27%). In the SMC, 1 out of 4 is post-AGB, and in the LMC, 3 out 11 are post-AGB objects. Thus, we can conclude that the selected region in the colour-colour diagram, while selecting the genuine post-AGB objects, overlaps severely with other types of objects, in particular young stellar objects and planetary nebulae. Additional classification criteria are required to distinguish between post-AGB stars and other types of objects. In particular, photometry at far-IR wavelengths would greatly assist in distinguishing young stellar objects from evolved ones. On the other hand, we showed that the low-resolution optical spectra appear to be sufficient to determine whether the candidates are post-AGB objects.

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Evolution of 1–5 Mm⊙ Stars by Mass Loss

Symposium - International Astronomical Union ◽

10.1017/s0074180900172110 ◽

1993 ◽

Vol 155 ◽

pp. 478-478

Author(s):

E. Vassiliadis ◽

P.R. Wood

Keyword(s):

Mass Loss ◽

Loss Rate ◽

Main Sequence ◽

Mass Loss Rate ◽

Star Clusters ◽

Magellanic Clouds ◽

Pulsation Period ◽

Agb Stars ◽

Loss Formula ◽

Loss Rates

Stars of mass 1–5 MM⊙ and composition Y=0.25 and Z=0.016 have been evolved from the main-sequence to the white dwarf stage with an empirical mass loss formula based on observations of mass loss rates in AGB stars. This mass loss formula (Wood 1990) causes the mass loss rate to rise exponentially with pulsation period on the AGB until superwind rates are achieved, where these rates correspond to radiation pressure driven mass loss rates. The formula was designed to reproduce the maximum periods observed for optically-visible LPVs and it also reproduces extremely well the maximum AGB luminosities observed in star clusters in the Magellanic Clouds (see Vassiliadis and Wood 1992 for details).

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Water masers and the near-stellar environment in YSOs

Symposium - International Astronomical Union ◽

10.1017/s0074180900222006 ◽

2002 ◽

Vol 206 ◽

pp. 27-34

Author(s):

Mark J. Claussen

Keyword(s):

Main Sequence ◽

Very Long Baseline Interferometry ◽

Angular Resolution ◽

Young Stellar Objects ◽

High Angular Resolution ◽

High Luminosity ◽

Stellar Objects ◽

Long Baseline ◽

Water Masers ◽

Very High

I present a review of observations of water masers, in particular very high angular resolution of water masers using Very Long Baseline Interferometry, with which it is possible to probe the environment of young stellar objects and forming stars within only a few A.U. of the protostar, its accretion disk, and therefore the base of outflowing material. Although reference is made to some high-luminosity sources, the main thrust of the review are the water masers found toward forming objects whose mass and luminosity will be approximately that of the Sun when they reach the main sequence.

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Energetics, Collimation and Propagation of Galactic Protostellar Outflows

Symposium - International Astronomical Union ◽

10.1017/s0074180900061684 ◽

1997 ◽

Vol 182 ◽

pp. 241-258 ◽

Cited By ~ 2

Author(s):

Max Camenzind

Keyword(s):

Main Sequence ◽

Young Stellar Objects ◽

Rotating Stars ◽

Main Sequence Stars ◽

Stellar Objects ◽

Central Object ◽

Protostellar Jets ◽

Bow Shocks ◽

Low Mass ◽

Rapidly Rotating Stars

Formation of jets in low-mass protostellar objects and young pre-main sequence stars is ultimately related to the existence of some gaseous disk around a rapidly rotating central object. This configuration has deep parallels to extragalactic systems such as radio galaxies and quasars. Rotating black holes are still thought to be the prime-mover behind the activity detected in centers of galaxies, while, in the case of protostellar jets, rapidly rotating stars and disks are responsible for the ejection of bipolar outflows. In both cases, magnetic fields are invoked for the acceleration, the collimation and propagation of these outflows. The ultimate rooting of these fields is still under debate. We discuss models where winds injected into rapidly rotating magnetospheres of the central object drive the outflows. From these considerations it follows that the jets of young stellar objects can only be produced magnetically and that their progagation is determined by their magnetic properties. Such jets have low Mach numbers ≃ 2 and their instabilities are dominated by the pinch mode. Knots closest to the source are attributed to compression by the time-dependent pinches. Multiple bow shocks occur on longer time-scales (a few thousand years) and are attributed to variations in the magnetospheric structure of the star, or the disk.

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