Spectroscopic analysis of accretion/ejection signatures in the Herbig Ae/Be stars HD 261941 and V590 Mon

ABSTRACT Herbig Ae/Be (HAeBe) stars are the intermediate-mass analogues of low-mass T Tauri stars. Both groups may present signs of accretion, outflow, and IR excess related to the presence of circumstellar discs. Magnetospheric accretion models are generally used to describe accreting T Tauri stars, which are known to have magnetic fields strong enough to truncate their inner discs and form accretion funnels. Since few HAeBe stars have had magnetic fields detected, they may accrete through a different mechanism. Our goal is to analyse the morphology and variability of emission lines that are formed in the circumstellar environment of HAeBe stars and use them as tools to understand the physics of the accretion/ejection processes in these systems. We analyse high-resolution (R ∼ 47 000) UVES/ESO spectra of two HAeBe stars – HD 261941 (HAe) and V590 Mon (HBe) that are members of the young (∼3 Myr) NGC 2264 stellar cluster and present indications of sufficient circumstellar material for accretion and ejection processes to occur. We determine stellar parameters with synthetic spectra, and also analyse and classify circumstellar lines such as H α, H β, and He i λ5875.7, according to their morphologies. We model the H α mean line profile, using a hybrid Magnetohydrodynamics (MHD) model that includes a stellar magnetosphere and a disc wind, and find signatures of magnetically driven outflow and accretion in HD 261941, while the H α line of V590Mon seems to originate predominantly in a disc wind.

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Observations of magnetic fields in Herbig Ae/Be stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003764 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 123-123

Author(s):

Markus Schöller ◽

Swetlana Hubrig

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

T Tauri Stars ◽

Be Stars ◽

T Tauri ◽

Weak Magnetic Fields ◽

Order Of Magnitude ◽

Field Geometry ◽

Herbig Ae Stars ◽

Magnetospheric Accretion

AbstractModels of magnetically driven accretion reproduce many observational properties of T Tauri stars. For the more massive Herbig Ae/Be stars, the corresponding picture has been questioned lately, in part driven by the fact that their magnetic fields are typically one order of magnitude weaker. Indeed, the search for magnetic fields in Herbig Ae/Be stars has been quite time consuming, with a detection rate of about 10% (e.g. Alecian et al. 2008), also limited by the current potential to detect weak magnetic fields. Over the last two decades, magnetic fields were found in about twenty objects (Hubrig et al. 2015) and for only two Herbig Ae/Be stars was the magnetic field geometry constrained. Ababakr, Oudmaijer & Vink (2017) studied magnetospheric accretion in 56 Herbig Ae/Be stars and found that the behavior of Herbig Ae stars is similar to T Tauri stars, while Herbig Be stars earlier than B7/B8 are clearly different. The origin of the magnetic fields in Herbig Ae/Be stars is still under debate. Potential scenarios include the concentration of the interstellar magnetic field under magnetic flux conservation, pre-main-sequence dynamos during convective phases, mergers, or common envelope developments. The next step in this line of research will be a dedicated observing campaign to monitor about two dozen HAeBes over their rotation cycle.

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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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Magnetic fields of T Tauri stars and inner accretion discs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003740 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 121-121

Author(s):

Jean-Francois Donati

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Near Infrared ◽

High Sensitivity ◽

T Tauri Stars ◽

Accretion Discs ◽

High Resolution Spectroscopy ◽

T Tauri ◽

Low Mass ◽

The Impact

AbstractMagnetic fields play a key role in the early life of stars and their planets, as they form from collapsing dense cores that progressively flatten into large-scale accretion discs and eventually settle as young suns orbited by planetary systems. Pre-main-sequence phases, in which central protostars feed from surrounding planet-forming accretion discs, are especially crucial for understanding how worlds like our Solar System are born.Magnetic fields of low-mass T Tauri stars (TTSs) are detected through high-resolution spectroscopy and spectropolarimetry (e.g., Johns Krull 2007), whereas their large-scale topologies can be inferred from time series of Zeeman signatures using tomographic techniques inspired from medical imaging (Donati & Landstreet 2009). Large-scale fields of TTSs are found to depend on the internal structure of the newborn star, allowing quantitative models of how TTSs magnetically interact with their inner accretion discs, and the impact of this interaction on the subsequent stellar evolution (e.g., Romanova et al. 2002, Zanni & Ferreira 2013).With its high sensitivity to magnetic fields, SPIRou, the new near-infrared spectropolarimeter installed in 2018 at CFHT (Donati et al. 2018), should yield new advances in the field, especially for young embedded class-I protostars, thereby bridging the gap with radio observations.

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Magnetic fields of weak line T-Tauri stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004100 ◽

2016 ◽

Vol 12 (S328) ◽

pp. 101-106

Author(s):

Colin A. Hill ◽

Keyword(s):

Magnetic Fields ◽

T Tauri Stars ◽

Doppler Imaging ◽

Mass Star ◽

Weak Line ◽

T Tauri ◽

Internal Structures ◽

Low Mass ◽

And Migration ◽

Pms Stars

AbstractT-Tauri stars (TTS) are late-type pre-main-sequence (PMS) stars that are gravitationally contracting towards the MS. Those that possess a massive accretion disc are known as classical T-Tauri stars (cTTSs), and those that have exhausted the gas in their inner discs are known as weak-line T-Tauri stars (wTTSs). Magnetic fields largely dictate the angular momentum evolution of TTS and can affect the formation and migration of planets. Thus, characterizing their magnetic fields is critical for testing and developing stellar dynamo models, and trialling scenarios currently invoked to explain low-mass star and planet formation. The MaTYSSE programme (Magnetic Topologies of Young Stars and the Survival of close-in Exoplanets) aims to determine the magnetic topologies of ~30 wTTSs and monitor the long-term topology variability of ~5 cTTSs. We present several wTTSs that have been magnetically mapped thus far (using Zeeman Doppler Imaging), where we find a much wider range of field topologies compared to cTTSs and MS dwarfs with similar internal structures.

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Magnetospheric accretion in the intermediate-mass T Tauri star HQ Tauri

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038086 ◽

2020 ◽

Vol 642 ◽

pp. A99 ◽

Cited By ~ 1

Author(s):

K. Pouilly ◽

J. Bouvier ◽

E. Alecian ◽

S. H. P. Alencar ◽

A.-M. Cody ◽

...

Keyword(s):

Magnetic Field ◽

Strong Magnetic Field ◽

Main Sequence ◽

T Tauri Stars ◽

Line Profiles ◽

Main Sequence Stars ◽

Intermediate Mass ◽

Accretion Process ◽

T Tauri ◽

Magnetospheric Accretion

Context. Classical T Tauri stars are pre-main sequence stars surrounded by an accretion disk. They host a strong magnetic field, and both magnetospheric accretion and ejection processes develop as the young magnetic star interacts with its disk. Studying this interaction is a major goal toward understanding the properties of young stars and their evolution. Aims. The goal of this study is to investigate the accretion process in the young stellar system HQ Tau, an intermediate-mass T Tauri star (1.9 M⊙). Methods. The time variability of the system is investigated both photometrically, using Kepler-K2 and complementary light curves, and from a high-resolution spectropolarimetric time series obtained with ESPaDOnS at CFHT. Results. The quasi-sinusoidal Kepler-K2 light curve exhibits a period of 2.424 d, which we ascribe to the rotational period of the star. The radial velocity of the system shows the same periodicity, as expected from the modulation of the photospheric line profiles by surface spots. A similar period is found in the red wing of several emission lines (e.g., HI, CaII, NaI), due to the appearance of inverse P Cygni components, indicative of accretion funnel flows. Signatures of outflows are also seen in the line profiles, some being periodic, others transient. The polarimetric analysis indicates a complex, moderately strong magnetic field which is possibly sufficient to truncate the inner disk close to the corotation radius, rcor ∼ 3.5 R⋆. Additionally, we report HQ Tau to be a spectroscopic binary candidate whose orbit remains to be determined. Conclusions. The results of this study expand upon those previously reported for low-mass T Tauri stars, as they indicate that the magnetospheric accretion process may still operate in intermediate-mass pre-main sequence stars, such as HQ Tauri.

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Magnetic fields of intermediate mass T Tauri stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731889 ◽

2017 ◽

Vol 608 ◽

pp. A77 ◽

Cited By ~ 11

Author(s):

A. Lavail ◽

O. Kochukhov ◽

G. A. J. Hussain ◽

E. Alecian ◽

G. J. Herczeg ◽

...

Keyword(s):

Magnetic Fields ◽

T Tauri Stars ◽

Intermediate Mass ◽

T Tauri

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Theoretical and observational aspects of young stars of intermediate mass

Symposium - International Astronomical Union ◽

10.1017/s0074180900199036 ◽

1991 ◽

Vol 147 ◽

pp. 331-344

Author(s):

Francesco Palla

Keyword(s):

Massive Stars ◽

Mass Range ◽

T Tauri Stars ◽

Young Stars ◽

Be Stars ◽

Surface Phenomena ◽

Intermediate Mass ◽

T Tauri ◽

Recent Developments ◽

Complex Phenomena

An account is given of the observational and theoretical properties that characterize young stars of intermediate-mass (2 ≤ M∗ / M⊙ ≤ 10), known as Herbig Ae/Be stars. The mass range of these objects is an interesting one, since it involves the occurrence of complex phenomena associated with the transition from fully convective configurations, typical of T Tauri stars, to radiatively stable objects, as in the case of massive stars. An overview of relevant observations testifying the variety of surface phenomena associated with the Herbig Ae/Be stars is presented. Recent developments in the theory of the formation on intermediate-mass protostars will also be discussed.

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Magnetic fields along the pre-main sequence: new magnetic field measurements of Herbig Ae/Be stars using high-resolution HARPS spectropolarimetry

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003843 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 134-134

Author(s):

S. P. Järvinen ◽

S. Hubrig ◽

M. Schöller ◽

I. Ilyin

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Field Measurements ◽

Be Stars ◽

Magnetic Studies ◽

Intermediate Mass Stars ◽

T Tauri ◽

Large Measurement ◽

Herbig Ae Stars ◽

Magnetospheric Accretion

AbstractHerbig Ae/Be-type stars are analogs of T Tauri stars at higher masses. Since the confirmation of magnetospheric accretion using Balmer and sodium line profiles in the Herbig Ae star UX Ori, a number of magnetic studies have been attempted, indicating that about 20 Herbig Ae/Be stars likely have globally organized magnetic fields. The low detection rate of magnetic fields in Herbig Ae stars can be explained by the weakness of these fields and rather large measurement uncertainties. The obtained density distribution of the root mean square longitudinal magnetic field values revealed that only a few stars have magnetic fields stronger than 200 G, and half of the sample possesses magnetic fields of about 100 G or less. We report on the results of our analysis of a sample of presumably single Herbig Ae/Be stars based on recent observations obtained with HARPSpol attached to ESO’s 3.6m telescope. Knowledge of the magnetic field structure combined with the determination of the chemical composition are indispensable to constrain theories on star formation and magnetospheric accretion in intermediate-mass stars. As of today, magnetic phase curves have been obtained only for two Herbig Ae/Be stars, HD 101412 and V380 Ori.

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On the Mass Accretion Rates of Herbig Ae/Be Stars. Magnetospheric Accretion or Boundary Layer?

Galaxies ◽

10.3390/galaxies8020039 ◽

2020 ◽

Vol 8 (2) ◽

pp. 39

Author(s):

Ignacio Mendigutía

Keyword(s):

Boundary Layer ◽

Magnetic Fields ◽

Young Stellar Objects ◽

Driving Mechanism ◽

Be Stars ◽

Stellar Objects ◽

Star Forming ◽

T Tauri ◽

Accretion Rates ◽

Magnetospheric Accretion

Understanding how young stars gain their masses through disk-to-star accretion is of paramount importance in astrophysics. It affects our knowledge about the early stellar evolution, the disk lifetime and dissipation processes, the way the planets form on the smallest scales, or the connection to macroscopic parameters characterizing star-forming regions on the largest ones, among others. In turn, mass accretion rate estimates depend on the accretion paradigm assumed. For low-mass T Tauri stars with strong magnetic fields there is consensus that magnetospheric accretion (MA) is the driving mechanism, but the transfer of mass in massive young stellar objects with weak or negligible magnetic fields probably occurs directly from the disk to the star through a hot boundary layer (BL). The intermediate-mass Herbig Ae/Be (HAeBe) stars bridge the gap between both previous regimes and are still optically visible during the pre-main sequence phase, thus constituting a unique opportunity to test a possible change of accretion mode from MA to BL. This review deals with our estimates of accretion rates in HAeBes, critically discussing the different accretion paradigms. It shows that although mounting evidence supports that MA may extend to late-type HAes but not to early-type HBes, there is not yet a consensus on the validity of this scenario versus the BL one. Based on MA and BL shock modeling, it is argued that the ultraviolet regime could significantly contribute in the future to discriminating between these competing accretion scenarios.

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