Measuring stellar magnetic fields from high resolution spectroscopy of near-infrared lines

Exoplanet research has shown an incessant growth since the first claim of a hot giant planet around a solar-like star in the mid-1990s. Today, the new facilities are working to spot the first habitable rocky planets around low-mass stars as a forerunner for the detection of the long-awaited Sun-Earth analog system. All the achievements in this field would not have been possible without the constant development of the technology and of new methods to detect more and more challenging planets. After the consolidation of a top-level instrumentation for high-resolution spectroscopy in the visible wavelength range, a huge effort is now dedicated to reaching the same precision and accuracy in the near-infrared. Actually, observations in this range present several advantages in the search for exoplanets around M dwarfs, known to be the most favorable targets to detect possible habitable planets. They are also characterized by intense stellar activity, which hampers planet detection, but its impact on the radial velocity modulation is mitigated in the infrared. Simultaneous observations in the visible and near-infrared ranges appear to be an even more powerful technique since they provide combined and complementary information, also useful for many other exoplanetary science cases.

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On the synergy between Ariel and ground-based high-resolution spectroscopy

Experimental Astronomy ◽

10.1007/s10686-021-09824-7 ◽

2022 ◽

Author(s):

Gloria Guilluy ◽

Alessandro Sozzetti ◽

Paolo Giacobbe ◽

Aldo S. Bonomo ◽

Giuseppina Micela

Keyword(s):

High Resolution ◽

Near Infrared ◽

Major Axis ◽

High Resolution Spectroscopy ◽

Correlation Technique ◽

Temperature Structure ◽

Low Resolution ◽

Semi Major Axis ◽

Species Discovery ◽

Orbital Parameters

AbstractSince the first discovery of an extra-solar planet around a main-sequence star, in 1995, the number of detected exoplanets has increased enormously. Over the past two decades, observational instruments (both onboard and on ground-based facilities) have revealed an astonishing diversity in planetary physical features (i. e. mass and radius), and orbital parameters (e.g. period, semi-major axis, inclination). Exoplanetary atmospheres provide direct clues to understand the origin of these differences through their observable spectral imprints. In the near future, upcoming ground and space-based telescopes will shift the focus of exoplanetary science from an era of “species discovery” to one of “atmospheric characterization”. In this context, the Atmospheric Remote-sensing Infrared Exoplanet Large (Ariel) survey, will play a key role. As it is designed to observe and characterize a large and diverse sample of exoplanets, Ariel will provide constraints on a wide gamut of atmospheric properties allowing us to extract much more information than has been possible so far (e.g. insights into the planetary formation and evolution processes). The low resolution spectra obtained with Ariel will probe layers different from those observed by ground-based high resolution spectroscopy, therefore the synergy between these two techniques offers a unique opportunity to understanding the physics of planetary atmospheres. In this paper, we set the basis for building up a framework to effectively utilise, at near-infrared wavelengths, high-resolution datasets (analyzed via the cross-correlation technique) with spectral retrieval analyses based on Ariel low-resolution spectroscopy. We show preliminary results, using a benchmark object, namely HD 209458 b, addressing the possibility of providing improved constraints on the temperature structure and molecular/atomic abundances.

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Characterising the surface magnetic fields of T Tauri stars with high-resolution near-infrared spectroscopy

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935695 ◽

2019 ◽

Vol 630 ◽

pp. A99 ◽

Cited By ~ 5

Author(s):

A. Lavail ◽

O. Kochukhov ◽

G. A. J. Hussain

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Magnetic Fields ◽

Large Scale ◽

Near Infrared ◽

Field Measurements ◽

T Tauri Stars ◽

Small Scale ◽

Surface Magnetic Field ◽

T Tauri

Aims. In this paper, we aim to characterise the surface magnetic fields of a sample of eight T Tauri stars from high-resolution near-infrared spectroscopy. Some stars in our sample are known to be magnetic from previous spectroscopic or spectropolarimetric studies. Our goals are firstly to apply Zeeman broadening modelling to T Tauri stars with high-resolution data, secondly to expand the sample of stars with measured surface magnetic field strengths, thirdly to investigate possible rotational or long-term magnetic variability by comparing spectral time series of given targets, and fourthly to compare the magnetic field modulus ⟨B⟩ tracing small-scale magnetic fields to those of large-scale magnetic fields derived by Stokes V Zeeman Doppler Imaging (ZDI) studies. Methods. We modelled the Zeeman broadening of magnetically sensitive spectral lines in the near-infrared K-band from high-resolution spectra by using magnetic spectrum synthesis based on realistic model atmospheres and by using different descriptions of the surface magnetic field. We developped a Bayesian framework that selects the complexity of the magnetic field prescription based on the information contained in the data. Results. We obtain individual magnetic field measurements for each star in our sample using four different models. We find that the Bayesian Model 4 performs best in the range of magnetic fields measured on the sample (from 1.5 kG to 4.4 kG). We do not detect a strong rotational variation of ⟨B⟩ with a mean peak-to-peak variation of 0.3 kG. Our confidence intervals are of the same order of magnitude, which suggests that the Zeeman broadening is produced by a small-scale magnetic field homogeneously distributed over stellar surfaces. A comparison of our results with mean large-scale magnetic field measurements from Stokes V ZDI show different fractions of mean field strength being recovered, from 25–42% for relatively simple poloidal axisymmetric field topologies to 2–11% for more complex fields.

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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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Observational methods for stellar magnetism: from detection to cartography

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313002913 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 447-458 ◽

Cited By ~ 1

Author(s):

Klaus G. Strassmeier ◽

Thorsten A. Carroll ◽

Ilya Ilyin ◽

Silva Järvinen

Keyword(s):

High Resolution ◽

Magnetic Fields ◽

Inverse Modeling ◽

Doppler Imaging ◽

Observational Methods ◽

Related Data ◽

Cool Stars ◽

Stellar Magnetic Fields

AbstractWe review some of the currently used techniques to detect stellar magnetic fields on cool stars. Emphasis is put on spectropolarimetry with high-resolution spectrographs and its related data de-noising techniques and multi-line inverse modeling. Detections and results from Zeeman splittings and broadenings are briefly mentioned. We discuss some of our most recent Zeeman Doppler Imaging (ZDI) results and present a comparison of ZDI maps of the K-type WTTS V410 Tauri and the planet-hosting F8 star HD 179949 with results from other groups.

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Near infrared high resolution spectroscopy and spectro-astrometry of gas in disks around Herbig Ae/Be stars

Astrophysics and Space Science ◽

10.1007/s10509-015-2260-4 ◽

2015 ◽

Vol 357 (1) ◽

Cited By ~ 8

Author(s):

Sean D. Brittain ◽

Joan R. Najita ◽

John S. Carr

Keyword(s):

High Resolution ◽

Near Infrared ◽

High Resolution Spectroscopy ◽

Be Stars

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Searching for H2 emission from protoplanetary disks using near- and mid-infrared high-resolution spectroscopy

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308016827 ◽

2007 ◽

Vol 3 (S249) ◽

pp. 359-368

Author(s):

A. Carmona ◽

M. E. van den Ancker ◽

Th. Henning ◽

Ya. Pavlyuchenkov ◽

C. P. Dullemond ◽

...

Keyword(s):

Surface Layer ◽

High Resolution ◽

Near Infrared ◽

Protoplanetary Disks ◽

High Resolution Spectroscopy ◽

Disk Model ◽

Mid Infrared ◽

T Tauri ◽

Hα Emission ◽

Ir Emission

AbstractThe mass and dynamics of protoplanetary disks are dominated by molecular hydrogen (H2). However, observationally very little is known about the H2. In this paper, we discuss two projects aimed to constrain the properties of H2 in the disk's planet forming region (R<50AU). First, we present a sensitive survey for pure-rotational H2 emission at 12.278 and 17.035 μm in a sample of nearby Herbig Ae/Be and T Tauri stars using VISIR, ESO's VLT high-resolution mid-infrared spectrograph. Second, we report on a search for H2 ro-vibrational emission at 2.1228, 2.2233 and 2.2477 μm in the classical T Tauri star LkHα 264 and the debris disk 49 Cet employing CRIRES, ESO's VLT high-resolution near-infrared spectrograph.VISIR project: none of the sources show H2 mid-IR emission. The observed disks contain less than a few tenths of MJupiter of optically thin H2 at 150 K, and less than a few MEarth at T>300 K. % and higher T. Our non-detections are consistent with the low flux levels expected from the small amount of H2 gas in the surface layer of a Chiang and Goldreich (1997) Herbig Ae two-layer disk model. In our sources the H2 and dust in the surface layer have not significantly departed from thermal coupling (Tgas/Tdust<2) and the gas-to-dust ratio in the surface layer is very likely <1000.CRIRES project: The H2 lines at 2.1218 μm and 2.2233 μm are detected in LkHα 264. An upper limit on the 2.2477 μm H2 line flux in LkHα 264 is derived. 49 Cet does not exhibit H2 emission in any of observed lines. There are a few MMoon of optically thin hot H2 in the inner disk (∼0.1 AU) of LkHα 264, and less than a tenth of a MMoon of hot H2 in the inner disk of 49 Cet. The shape of the 1–0 S(0) line indicates that LkHα disk is close to face-on (i<35o). The measured 1–0 S(0)/1–0 S(1) and 2–1 S(1)/1–0 S(1) line ratios in LkHα 264 indicate that the H2 is thermally excited at T<1500 K. The lack of H2 emission in the NIR spectra of 49 Cet and the absence of Hα emission suggest that the gas in the inner disk of 49 Cet has dissipated.

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