EXTENDED MAGNETOSPHERES IN PRE-MAIN-SEQUENCE EVOLUTION: FROM T TAURI STARS TO THE BROWN DWARF LIMIT

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.

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Finding orbital motion of sub-stellar companions - the case of TWA 5B

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308018851 ◽

2007 ◽

Vol 3 (S248) ◽

pp. 126-127 ◽

Cited By ~ 1

Author(s):

T. Schmidt ◽

R. Neuhäuser ◽

M. Mugrauer

Keyword(s):

Proper Motion ◽

Main Sequence ◽

Orbital Motion ◽

T Tauri Stars ◽

Brown Dwarf ◽

T Tauri ◽

Combining Data ◽

Tw Hydrae Association ◽

Astrometric Data ◽

Triple Star

AbstractTWA 5B is a brown dwarf companion of H=12 mag, 2″ off the ~5 mag brighter triple star CoD-33° 7795 (=TWA 5), a member of the TW Hydrae association of T Tauri stars at ~55 pc. This object is the first brown dwarf around a pre-main-sequence star (confirmed by common proper motion) ever found. In the last year we have newly reduced VLT NaCo data originally taken in 2003 and combined it with all the available astrometric data of the system to investigate possibly detectable orbital motion of the system. Indeed we were able to find linear orbital motion of the system combining data from HST, VLT and Gemini-North.

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Dynamical Masses of T Tauri Stars and Calibration of Pre–Main‐Sequence Evolution

The Astrophysical Journal ◽

10.1086/317838 ◽

2000 ◽

Vol 545 (2) ◽

pp. 1034-1043 ◽

Cited By ~ 328

Author(s):

M. Simon ◽

A. Dutrey ◽

S. Guilloteau

Keyword(s):

Main Sequence ◽

T Tauri Stars ◽

Sequence Evolution ◽

T Tauri ◽

Dynamical Masses

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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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Spectral energy distributions and structures of debris discs

Symposium - International Astronomical Union ◽

10.1017/s0074180900218159 ◽

2004 ◽

Vol 202 ◽

pp. 328-330

Author(s):

W.R.F. Dent ◽

M. C. Wyatt ◽

W. S. Holland ◽

J. S. Greaves ◽

I. M. Coulson ◽

...

Keyword(s):

Main Sequence ◽

T Tauri Stars ◽

Spectral Energy ◽

Spectral Energy Distributions ◽

Energy Distributions ◽

Long Wavelength ◽

T Tauri

New photometry of main-sequence debris discs has been carried out at 850 and 450/μm; the derived SEDs indicate that the dust can lie in either thin rings or radially-extended discs, as seen directly in the few nearby objects which are resolvable. All such objects are consistent with a long wavelength opacity index β of 1.0±0.2 - similar to T Tauri stars, but significantly lower than embedded objects.

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UV-Observations of Young Populous Clusters in the Large Magellanic Cloud

Symposium - International Astronomical Union ◽

10.1017/s0074180900039929 ◽

1984 ◽

Vol 108 ◽

pp. 55-56

Author(s):

Edward H. Geyer ◽

Angelo Cassatella

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Large Magellanic Cloud ◽

Time Interval ◽

Sequence Evolution ◽

Stellar Clusters ◽

T Tauri ◽

Red Supergiants ◽

Evolution Phase ◽

Massive Clusters

The young populous star clusters give evidence for the ‘explosive’ star formation in the Magellanic Clouds which took place in the time interval 5·106 yrs to < 108 yrs agoe. They are also key objects for the understanding of the formation of massive stellar clusters, because they are still situated close to their ‘birthplace’ in the parent galaxy and are dynamically not relaxed (Geyer et al. 1979). Their HRD-morphology shows most of the member stars in the upper Main Sequence range with only a few massive yellow and red supergiants. The lower massive stars are still in the pre-main-sequence evolution phase (‘T-Tauri state’), which cannot be observed at the MC's distances. Thus in the uv-spectral range the blue stars with (B-V) < 0.1 on the upper MS contribute to the uv-fluxes. In the optical spectral regions the bright ‘blue’ globular clusters seem not be embedded in remanent interstellar matter, though neighbouring loose stellar aggregates of similar age are in many cases surrounded by dense HII-regions. This rises the questions wether the starformation process in such massive clusters was so efficient that no remanent matter was left over, or was this material blown away by the uv-radiation of the numerous OB-member stars?

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Magnetic fields of intermediate-mass T Tauri stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833545 ◽

2019 ◽

Vol 622 ◽

pp. A72 ◽

Cited By ~ 17

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.

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Brown dwarf jets: Investigating the universality of jet launching mechanisms at the lowest masses

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310016467 ◽

2010 ◽

Vol 6 (S275) ◽

pp. 396-399

Author(s):

Emma Teresa Whelan ◽

Francesca Bacciotti ◽

Tom Ray ◽

Catherine Dougados

Keyword(s):

Accretion Rate ◽

T Tauri Stars ◽

Brown Dwarf ◽

Central Mass ◽

Mass Accretion Rate ◽

T Tauri ◽

Mass Outflow ◽

The Common ◽

Protostellar Objects

AbstractRecently it has become apparent that proto-stellar-like outflow activity extends to the brown dwarf (BD) mass regime. While the presence of accretion appears to be the common ingredient in all objects known to drive jets fundamental questions remain unanswered. The more prominent being the exact mechanism by which jets are launched, and whether this mechanism remains universal among such a diversity of sources and scales. To address these questions we have been investigating outflow activity in a sample of protostellar objects that differ considerably in mass and mass accretion rate. Central to this is our study of brown dwarf jets. To date Classical T Tauri stars (CTTS) have offered us the best touchstone for decoding the launching mechanism. Here we shall summarise what is understood so far of BD jets and the important constraints observations can place on models. We will focus on the comparison between jets driven by objects with central mass <0.1M⊙ and those driven by CTTSs. In particular we wish to understand how the the ratio of the mass outflow to accretion rate compares to what has been measured for CTTSs.

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