scholarly journals High S/N Spectroscopy of Pre-Main Sequence Stars I

1988 ◽  
Vol 132 ◽  
pp. 87-93
Author(s):  
I. Appenzeller
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Circumstellar Disks ◽  
Circumstellar Matter ◽  
Spectroscopic Measurement ◽  
Spectral Lines ◽  
Stellar Winds ◽  
Main Sequence Stars ◽  
Pms Stars ◽  
Very High

The spectra of PMS stars usually are superpositions of contributions from a relatively normal photosphere, an often strongly enhanced chromosphere, and of circumstellar matter related to stellar winds, accreation flows, jets, and cool circumstellar disks. Only high S/N data allows a reliable separation of these different contributions. Because of the high optical depths of PMS chromospheres, the PMS photospheres often can be observed in the very weak spectral lines only, which are undectable on low S/N spectrograms. Finally, magnetic fields are assumed to play a particularly important role for the appearance and evolution of PMS objects. Their spectroscopic measurement requires very high S/N data.

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.

scholarly journals 29. Stellar Spectra

1985 ◽  
Vol 19 (1) ◽  
pp. 353-374
Author(s):  
J. Jugaku ◽  
G. Cayrel de Strobel ◽  
Y. Andrillat ◽  
W. K. Bonsack ◽  
P. S. Conti ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Circumstellar Matter ◽  
Magellanic Clouds ◽  
Be Stars ◽  
Main Sequence Stars ◽  
Stellar Spectra ◽  
Stellar Magnetic Fields

During the triennium under review, Commission 29 has sponsored or cosponsored the following IAU meetings: Symposium 102, “Solar and Stellar Magnetic Fields,” Zurich, Switzerland, August 1982; Symposium 108, “Structure and Evolution of the Magellanic Clouds,” Tübingen, FRG, September 1983; Symposium 111, “Calibration of Fundamental Stellar Quantities,” Como, Italy, May 1984; and Colloquium 82, “Cepheids: Observation and Theory,” Toronto, Canada, May-June 1984. Commission 29 has also supported or sponsored several IAU meetings proposed for 1985 and 1986. They include “Luminous Stars and Associations in Galaxies,” Porto Heli, Greece, May 1985; “Upper Main Sequence Stars with Anomalous Abundances,” Crimea, USSR, May 1985; “Astrochemistry,” Goa, India, December 1985; “Hydrogen Deficient Stars and Related Objects,” Bangalore, India, December 1985; “Circumstellar Matter,” Heidelberg, FRG, June 1986; and “Be Stars,” Boulder, USA, August 1986.

scholarly journals IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys

2009 ◽  
Vol 5 (H15) ◽  
pp. 815-815
Author(s):  
Antonio S. Hales ◽  
Michael J. Barlow ◽  
Janet E. Drew ◽  
Yvonne C. Unruh ◽  
Robert Greimel ◽  
...  
Keyword(s):  
Cross Correlation ◽  
Main Sequence ◽  
Terrestrial Planet ◽  
Circumstellar Disks ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Mid Infrared ◽  
Isaac Newton ◽  
Intermediate Mass Stars ◽  
Dust Disks

AbstractThe Isaac Newton Photometric H-Alpha Survey (IPHAS) provides (r′-Hα)-(r′-i′) colors, which can be used to select AV0-5 Main Sequence star candidates (age~20-200 Myr). By combining a sample of 23050 IPHAS-selected A-type stars with 2MASS, GLIMPSE and MIPSGAL photometry we searched for mid-infrared excesses attributable to dusty circumstellar disks. Positional cross-correlation yielded a sample of 2692 A-type stars, of which 0.6% were found to have 8-μm excesses above the expected photospheric values. The low fraction of main sequence stars with mid-IR excesses found in this work indicates that dust disks in the terrestrial planet zone of Main Sequence intermediate mass stars are rare. Dissipation mechanisms such as photo-evaporation, grain growth, collisional grinding or planet formation could possibly explain the depletion of dust detected in the inner regions of these disks.

scholarly journals Dust spreading in debris discs: do small grains cling on to their birth environment?

2019 ◽  
Vol 487 (4) ◽  
pp. 5874-5888 ◽  
Author(s):  
Nicole Pawellek ◽  
Attila Moór ◽  
Ilaria Pascucci ◽  
Alexander V Krivov
Keyword(s):  
Main Sequence ◽  
Angular Resolution ◽  
Spatial Location ◽  
Stellar Winds ◽  
Main Sequence Stars ◽  
Gravitational Forces ◽  
James Webb Space Telescope ◽  
Ring Location ◽  
Small Grains ◽  
Birth Environment

ABSTRACT Debris discs are dusty belts of planetesimals around main-sequence stars, similar to the asteroid and Kuiper belts in our Solar system. The planetesimals cannot be observed directly, yet they produce detectable dust in mutual collisions. Observing the dust, we can try to infer properties of invisible planetesimals. Here, we address the question of what is the best way to measure the location of outer planetesimal belts that encompass extrasolar planetary systems. A standard method is using resolved images at millimetre wavelengths, which reveal dust grains with sizes comparable to the observational wavelength. Smaller grains seen in the infrared (IR) are subject to several non-gravitational forces that drag them away from their birth rings, and so may not closely trace the parent bodies. In this study, we examine whether imaging of debris discs at shorter wavelengths might enable determining the spatial location of the exo-Kuiper belts with sufficient accuracy. We find that around M-type stars the dust best visible in the mid-IR is efficiently displaced inwards from their birth location by stellar winds, causing the discs to look more compact in mid-IR images than they actually are. However, around earlier-type stars where the majority of debris discs is found, discs are still the brightest at the birth ring location in the mid-IR regime. Thus, sensitive IR facilities with good angular resolution, such as MIRI on James Webb Space Telescope, will enable tracing exo-Kuiper belts in nearby debris disc systems.

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 Circumstellar Disks and Star Formation

1992 ◽  
Vol 9 ◽  
pp. 377-380
Author(s):  
L. Hartmann ◽  
M. Gomez ◽  
S.J. Kenyon
Keyword(s):  
Star Formation ◽  
Spectral Region ◽  
Main Sequence ◽  
Circumstellar Disks ◽  
Central Star ◽  
Disk Accretion ◽  
Main Sequence Stars ◽  
Excess Emission ◽  
Infrared Spectral ◽  
The Masses

Results from the IRAS satellite showed that many pre-main sequence stars exhibited unexpectedly large fluxes in the infrared spectral region. Several studies have shown that the simplest and most satisfying explanation of this excess emission is that it arises in optically-thick, dusty, circumstellar disks (Rucinski 1985; Adams, Lada, and Shu 1987, 1988; Kenyon and Hartmann 1987; Bertout, Basri, and Bouvier 1988; Basri and Bertout 1989). The masses of these disks are estimated to range between 10-3M⊙ to 1M⊙ (Beckwith et al. 1990; Adams et al. 1990), large enough that disk accretion may have a significant effect on the evolution of the central star. Indeed, Mercer-Smith, Cameron, and Epstein (1984) suggested that stars are essentially completely accreted from disks, rather than formed from quasi-spherical accretion (Stabler 1983, 1988).

scholarly journals Photospheric and “Chromospheric” CIV Lines in B-Main-Sequence Stars

1986 ◽  
Vol 116 ◽  
pp. 113-116
Author(s):  
Fiorella Castelli ◽  
Carlo Morossi ◽  
Roberto Stalio
Keyword(s):  
High Temperature ◽  
Stellar Wind ◽  
High Velocity ◽  
Main Sequence ◽  
Stellar Atmosphere ◽  
Uv Spectra ◽  
Spectral Lines ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars

The presence in the far-UV spectra of early-type stars of spectral lines of superionized atoms is argument of controversial debate among astronomers. Presently there is agreement on the non-radiative origin of these ions but not on the proposed mechanisms for their production nor on the proposed locations in the stellar atmosphere where they are abundant. Cassinelli et al. (1978) suggest that the Auger mechanism is operative in a cool wind blowing above a narrow corona to produce these ions; Lucy and White (1980) introduce radiative instabilities growing into hot blobs distributed across the stellar wind; Doazan and Thomas (1982) make these ions to be formed in both pre- and post-coronal, high temperature regions at low and high velocity respectively.

scholarly journals A Rotational Period Study of a Large Sample of Pre-Main Sequence stars in NGC 2264

2004 ◽  
Vol 215 ◽  
pp. 125-126 ◽  
Author(s):  
M. Lamm ◽  
C.A.L. Bailer-Jones ◽  
R. Mundt ◽  
W. Herbst
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
Monitoring Program ◽  
Bimodal Distribution ◽  
Main Sequence Stars ◽  
Lower Mass ◽  
Rotation Periods ◽  
Photometric Monitoring ◽  
Pms Stars ◽  
Mass Dependent

We present the results of a photometric monitoring program of pre-main sequence (PMS) stars in the young (2-4 Myr) open cluster NGC 2264 (d=700 pc). We find that the rotation periods are mass dependent and show a bimodal distribution for higher mass stars with M ≳ 0.3 M⊙ and a unimodal distribution for lower mass stars with M ≲ 0.3 M⊙.

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