Zobrazení hvězd: pomocí spekroskopie ve vysokém rozlišení a interferometrie na dlouhých základnách

• Thesis title in Czech: Zobrazení hvězd: pomocí spekroskopie ve vysokém rozlišení a interferometrie na dlouhých základnách
• Thesis title in English: Stars at a glance: with high-resolution spectroscopy and long-baseline interferometry
• Key words: stelární astronomie|spektroskopie|interferometrie
• English key words: stellar astronomy|spectroscopy|interferometry
• Academic year of topic announcement: 2021/2022
• Thesis type: dissertation
• Department: Student Affairs Department (32-STUD)
• Supervisor: doc. Mgr. Miroslav Brož, Ph.D.
• Author: hidden - assigned and confirmed by the Study Dept.
• Date of registration: 14.09.2021
• Date of assignment: 14.09.2021
• Confirmed by Study dept. on: 14.09.2021
• Advisors: prof. RNDr. Petr Harmanec, DrSc.

Guidelines

In the last years, compact stellar systems or systems with circumstellar matter can be studied with extensive datasets, including astrometry, photometry, spectroscopy, spectral-energy distribution (SED), interferometric visibility, closure phase, triple product, differential visibility, or differential phase. To interpret these sophisticated observations, a sufficiently complex and precise photo-dynamical models are needed. In this work, we suggest to study at least several stellar systems, using modelling tools like Xitau (Nemravova et al. 2016, Broz 2017), Pyshellspec (Mourard et al. 2018, Broz et al. 2021), Phoebe 2 (Prsa et al. 2020, Conroy et al. 2020), or their alternatives.

Extensive datasets already exists, e.g., for: δ Ori, ω CMa, V923 Aql, β Lyr, HD 152246, ξ Tau, or λ Tau. A brief description of these systems is attached below. In particular, there are new high-precision light curves from MOST, TESS, BRITE, interferometry from VEGA/CHARA, MIRC/CHARA, VLTI/AMBER, and spectroscopy from VLT/CRIRES, 2.2m FEROS, 3.6m HARPS, IUE, as found in the ESO and MAST archives. Consequently, a student should understand details of these observations, their uncertainties and systematics, even though the ultimate goal is a theoretical understanding of the systems.

Of course, it is necessary to continue with the development of our modelling tools (in Fortran, Python programming languages). For example, there are azimuthal asymmetries (spiral arms), or long-term temporal variability; it is useful to implement the subplex (Rowan 1990) or Powell's methods to improve a convergence; synthetic spectra have to be computed for non-standard chemical composition, e.g., with the Tlusty program (Hubeny & Lanz 1995, Hubeny & Lanz 2017); for hot star it may be necessary to use synthetic spectra for atmospheres with winds (FASTWIND or CMFGEN, Puls et al. 2020); alternatively, a Bayesian formulation is possible for problems studied previously by frequentist approach (or chi^2).

For systems having spectroscopic observations with a full phase coverage, or interferometric observation with a sufficient (u,v)-plane coverage, the inverse problem can be solved by unconstrained methods (Doppler tomography, inverse Fourier transform). Ideally, they should agree with geometrically-constrained models, but the real world is not ideal. As a result, a student should be able to construct complex models (of stellar systems), which is useful general knowledge.

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All systems include a hot star. δ Ori (HD 36486, HR 1852, HIP 25930) is a multiple system consisting of six gravitationally-bound stars (denoted Aa1, Aa2, Ab, B, C1, C2; Oplistilova et al. 2020). Component A consists of a detached eclipsing binary (P = 5.732436 d), and a more distant tertiary (P ~ 10^3 d).

The ω CMa and V923 Aql systems are Be stars - exhibiting long-term changes in radial velocity, V/R ratio, the Balmer emission lines, brightness, and colour. ω CMa (28 CMa, HD 56139, HR 2749, HIP 35037) might be binary, as inferred from its period analysis, and V923 Aql (HD 183656, HR 7415, HIP 95929) is a confirmed binary, with P = 214.716 d (Wolf et al. 2021).

The β Lyr system (HD 174638, HR 7106, HIP 92420) consists of six components in total. In the centre, there is a semidetached eclipsing binary with an optically thick accretion disk and thin circumstellar matter, creating strong emission lines (Broz et al. 2021). The remaining components are single stars.

HD 152246 (HIP 82685) is a triple system consisting of a close binary (O-type stars) with a slightly eccentric orbit (e = 0.11) and period P = 6.0049 d, which revolves in a 470-day highly eccentric orbit (e = 0.87) with another massive and bright component (Nasseri et at. 2014).

ξ Tauri (HD 21364, HR 1038, HIP 16083) is a hierarchical quadruple system. Three components are B-type main sequence dwarfs. Two of them form a detached eclipsing binary (P = 7.15 d), the third one has a period of 145 days, and the fourth one about fifty years (Nemravova et al. 2016).

Finally, λ Tauri (HD 25204, HR 1239, HIP 18724) is one of the most compact and strongly interacting stellar systems. The inner pair - a semidetached binary - with a period of only 3.95 days, is orbited by the third component every 33.025 days (Berdyugin et al. 2018).

References

Berdyugin et al. 2018
Broz et al. 2021
Conroy et al. 2020
Hubeny & Lanz 1995
Hubeny & Lanz 2017
Mourard et al. 2018
Nasseri et al. 2014
Nemravova et al. 2016
Oplistilova et al. 2020
Prsa et al. 2020
Puls et al. 2020
Rowan 1990
Wolf et al. 2021