Miroshnichenko Anatoly

Research Program in Star Formation

The program is devoted to investigation of the pre-main-sequence evolution. It is aimed at a search for new pre-main-sequence star candidates and quantitative criteria of separation of young and evolved stars; studies of the evolution of circumstellar envelopes, the role of binarity, and conditions for planet formation; modeling of the observed features; and constraining the structure of circumstellar envelopes. It includes (but is not limited to) the following projects.
 

Structure and physical properties of circumstellar envelopes around pre-main-sequence stars

The evolution of infrared excesses of pre-main-sequence Ae/Be and main-sequence A-type stars was studied (Miroshnichenko et al. 1996, Astron. Rep., 40, 509). A scenario of the evolution of dusty envelopes around young stars with masses of 2-4 Msun was proposed. A new model for dusty envelopes of pre-main-sequence Herbig Ae/Be stars was developed (Miroshnichenko et al. 1999, ApJ, 520, L115). The model implies co-existence of geometrically thin disks and extended halos and explains both spectral energy distributions and image sizes in a wide wavelength range (from UV to the millimeter wavelengths).

Future plans: Modeling of the SEDs and images at different wavelengths of a large sample of pre-main-sequence stars as well as new imaging observations are planned. The evolution of circumstellar envelopes of T Tau and Herbig Ae/Be stars with the same initial mass will be studied to put more constrains on the properties of both disks and halos.

Collaborations: M. Elitzur and D. Vinkovic (Univ. of Kentucky), Z.Ivezic (Princeton Univ.)
 

Refining physical parameters of Herbig Ae/Be stars

High-resolution spectroscopy (resolving power 15000-80000) at the 6-meter telescope of the Russian Academy of Sciences and the 2.1-meter Otto Struve telescope of the McDonald Observatory has been obtained for more than 20 Herbig Ae/Be stars since 1999. First results show that they may have metal-deficient atmospheres (Miroshnichenko et al. 2001, A&A, 377, 854). The data analysis is in progress.

Future plans: More observations are planned for the next 2 years. A proposal to obtain high-resolution (R ~ 100000) spectra of a sample of bright Herbig Ae/Be stars in the near-UV region at CFHT was submitted in 2003. Southern stars will be observed at the 2.1-meter telescope of the Complejo Astronomico El Leoncito (Argentina). Fundamental parameters and chemical composition will be determined for most of the known Herbig Ae/Be stars. The fraction of binary systems among these objects will be further constrained, impact of binarity on the properties of the circumstellar environments will be investigated.

Collaborations: K.S. Bjorkman (Univ. of Toledo), R.O. Gray (Apallachian State Univ.), V.G. Klochkova and V.E.Panchuk (Special Astrophys. Observatory of the Russian Academy of Sciences), H. Levato (Complejo Astronomico El Leoncito, Argentina), M.A. Pogodin (Pulkovo Observatory, Russia), N. Manset (CFHT Corp.)
 

Large-scale optical/infrared surveys to search for distant pre-main-sequence stars and star forming regions

Almost all known pre-main-sequence stars are located within 1 kpc from the Sun. In 2002 a deep multicolor survey (limiting V-band brightness ~ 22 mag.) of galactic star forming regions was started at the 3.6-m CFHT to search for pre-main-sequence star candidates at larger distances. First data for 9 regions in the optical bandpasses have been obtained so far and are being reduced.

Future plans: More star forming regions are planned for observations in the next few years. Emission-line stars will be separated on the basis of the Halpha filter images, objects with IR excesses will be separated on the basis of forthcoming near-IR imaging photometry, individual pre-main-sequence candidates will be observed with high-resolution spectroscopy.

Collaborations: N. Manset (CFHT Corp.) and P. Bastien (Univ. of Montreal)
 

New observational techniques and instrumentation

In 2000-2001 in collaboration with a group from the Special Astrophysical Observatory of the Russian Academy of Sciences I was involved in the design of the first high-resolution (R=15000) optical echelle-spectropolarimeter for the 6-meter Russian telescope. The instrument is capable of measuring linear polarization in both spectral lines and continuum in a broad spectral range (~3500-9000 A). The instrument and data reduction software were created, and the first observations were obtained.

Future plans: Using the experience from this project, our team is going to create a new device to achieve a better spectral resolution (R ~ 60000) and measure all 4 Stokes parameters.  Observations of a large sample of pre-main-sequence stars are planned in 2004-2005.

Collaborations: V.G. Klochkova and V.E.Panchuk (Special Astrophys. Observatory of the Russian Academy of Sciences), K.S. Bjorkman (Univ. of Toledo)
 

Studies of the most massive pre-main-sequence binaries

The upper mass limit for stars to have the observable pre-main-sequence stage, which is a crucial test for pre-main-sequence evolutionary theories, it is not clear yet. Moreover, more than a half of early B-type pre-main-sequence star candidates were found to be binaries. However, none of them has been studied in detail. We found one of them (HD 200775, Miroshnichenko et al. 1998, PASP, 110, 883) and derived the orbital period (3.68 years). A proposal for Chandra was submitted to study its X-ray behavior at the minimum activity phase to shed light on the secondary's properties.

Future plans: Spectroscopic and photometric observations to constrain orbital periods and parameters of the secondaries in other pre-main-sequence binaries are planned. Other earliest type stars will be observed to check for binarity.

Collaborations: V.G. Klochkova and V.E.Panchuk (Special Astrophys. Observatory of the Russian Academy of Sciences), K.S. Bjorkman (Univ. of Toledo), N. Manset (CFHT Corp.), M.A. Pogodin (Pulkovo Observatory, Russia), K.S.Kuratov (Tien-Shan Observatory, Kazakhstan), A.V. Kusakin (Sternberg Astronomical Institute, Russia), V. Airapetian (GSFC), V.V. Makarov (CalTech)
 

Studies of pre-main-sequence F-star candidates

Searches in the IRAS and 2MASS catalogs revealed a significant number of late A-type - F-type emission-line stars, which are thought to be pre-main-sequence objects. This is not unexpected, taking into account the slope of the initial mass function. At the same time, there is a controversy about the evolutionary state of these objects. As our first results of high-resolution spectroscopy show, they can be evolved giants, more luminous than the current theory predicts for young stars.

Future plans: High-resolution spectroscopic observations of a large sample of F-type pre-main-sequence and Vega-type candidates are planned at a number of telescopes (e.g., the 6-m Russian telescope, 2.1-m Otto Struve telescope). The behavior of the IR excesses in comparison with the basic stellar parameters will be studied.

Collaborations: V.G. Klochkova and V.E. Panchuk (Special Astrophys. Observatory of the Russian Academy of Sciences), K.S. Bjorkman (Univ. of Toledo), S.L.A. Vieira (Univ. Federal Minas Gerais, Brazil), A.A. Suchkov (STSci), R.O. Gray (Apallachian State Univ.), K.S. Kuratov (Tien-Shan Observatory, Kazakhstan), A.V. Kusakin (Sternberg Astronomical Institute, Russia)
 

Summarizing information about pre-main-sequence stars

The number of pre-main-sequence stars is not well known yet even in the solar neighbourhood. Four new Herbig Ae/Be candidate stars have been discovered cross- correlating optical position catalogs and IRAS Point and Faint Source catalogs (e.g., Miroshnichenko et al. 1999, A&A, 347, 137).

Future plans: Optical and near-IR photometric observations will be obtained for newly found and poorly studied objects. Additional searches for new pre-main-sequence candidates in the IRAS, MSX, and 2MASS catalogs are planned. A new catalog of Herbig Ae/Be stars with newly determined stellar and circumstellar parameters will be compiled to replace the latest one, published 10 years ago.

Collaborations: S.L.A. Vieira (Univ. Federal Minas Gerais, Brazil), K.S. Bjorkman (Univ. of Toledo),K.S.Kuratov (Tien-Shan Observatory, Kazakhstan), A.V. Kusakin (Sternberg Astronomical Institute, Russia)

 

Studies of emission-line stars with properties similar to those of pre-main-sequence stars

A number of emission-line stars similar to pre-main-sequence stars have not been proven to young. Their detailed observations are important to discriminate young and evolved objects, to study mass loss and dust formation mechanisms, to refine catalogs of pre-main-sequence objects, etc.  A long-term program focused on objects with strong emission-line spectra and IR excesses, which have previously been classified as evolved objects or unclassified, has been started (Miroshnichenko et al. 2002, ASP Conf. Ser., 279, 303).

Future plans: Photometric and spectroscopic observations of a group of B[e] stars and unclassified objects with large infrared excesses are planned to compare their properties with those of pre-main-sequence stars.

Collaborations: K.S. Bjorkman (Univ. of Toledo),T.L. Gandet (Lizard Hollow Observatory, Arizona), K.S.Kuratov (Tien-Shan Observatory, Kazakhstan), A.V. Kusakin (Sternberg Astronomical Institute, Russia), V.G. Klochkova and V.E.Panchuk (Special Astrophys. Observatory of the Russian Academy of Sciences), H. Levato (Complejo Astronomico El Leoncito, Argentina) R.J. Rudy and D.K. Lynch (Aerospace Corp.)