Exposure of details of the formation of massive stars
Zusammenfassung der Projektergebnisse
This project aimed at studying details in the formation of massive stars, especially the role of disks. In contrast to low-mass stars (≤2 M⊙ ), the formation of intermediate-mass and massive stars (≥8–10 M⊙ ) is much less understood. While current theory supports that massive stars form similar to their low-mass counterparts by accretion via circumstellar disks, few observations exist to confirm this process. Since disks are the birthplace of planets, their properties are intimately linked to the question of planet formation around massive stars. Moreover, spatially resolved observation of a disk is one of the few ways to obtain precise estimates of the central object’s mass. The lack of observational evidence is due to the special difficulties of observing massive stars in their earliest life phases: they are rare and therefore on average at large distance, they are obscured by gas and dust during the whole formation phase, and located usually in complex environments as dense stellar clusters. High spatial resolution and sensitivity as provided by radio interferometers is therefore necessary to study the details of the formation of such massive objects. In this project, the gas and dust in the close environment of the advantageously isolated and relatively nearby (1 kpc) young intermediate-mass object AFGL 490 was studied. Previous observations in the molecular line C17 O(2–1) had revealed a ca. 1 M⊙ and 1500 au wide circumstellar disk. Here, observations of CS(1– 0), C34 S(2–1) and four transitions of CH3 OH with high spatial resolution (1–2 ′′ ) taken by the interferometers Plateau de Bure and Very Large Array were analyzed. All transitions show emission in a region of 2000 au around AFGL 490, the presence of red- and a blueshifted velocity components indicates rotation, and therefore supports the earlier C17 O disk detection. To derive information about the disk structure, models of disks with a range of sizes, masses and around different central stars were constructed, the expected line emission calculated with a radiative transfer code, and finally compared with the observations. The modeling yields a similar central star (8–13 M⊙ ) and disk mass (0.4–1.3 M⊙ ), but a somewhat higher inclination angle (40–70 ◦ ) than the previous C17 O observations. However, the uncertainty of the results in this project is larger due to a lower spatial resolution and/or more weak transitions than those observed by Schreyer et al. (2006). Furthermore, C34 S, CS and CH3 OH shows emission in the wider environment of AFGL 490 (5–30 ′′ , corresponding to 5000–30000 au), originating from the dense walls of the outflow cavities. These high-resolution observations show the form of the inner outflow region: cones consisting of parabolic shells with a wide opening angle. The position angle of the outflow axis is with 39 ◦ close to the symmetry axis of the inner disk. The inclination angle suggested by the outflow is high with 80 ◦ , although a low-inclination case with 40 ◦ cannot be completely ruled out. Although one of the key questions regarding AFGL 490, the inclination angle of the disk, could not be answered conclusively, the observations show several interesting aspects: The C34 S and CS observations indicate a smaller disk radius (700–1100 au) than the previous C17 O measurements (ca. 1500 au), which in terms of the used model points to CS and its isotope being more concentrated in the inner regions of the disk, and is therefore a first hint on the disk’s chemical structure. The region between the disk (≤2000 au) and the outflow shells (≥5000 au) is devoid of emission, which was not resolved in earlier observations. This observation supports theoretical simulations in which the infalling gas from the envelope is shocked at the outflow walls and accretes onto the inner disk only through a thin channel in the equatorial plane. A further hint on such infall from the envelope towards the disk is the detection of peculiar (inverse P-Cygni-like) line profiles both close to the central disk and to the outflow walls.
Projektbezogene Publikationen (Auswahl)
- Observation of Young Stars at the University Observatory Jena. 2011, ASPC 448, 553
Berndt, A., Errmann, R., Maciejewski, G., Raetz, St., Marka, C., Ginski, Ch., Mugrauer, M., Schmidt, T. O. B., Neuhäuser, R., Seeliger, M., Moualla, M., Pribulla, T., Hohle, M. M., Tetzlaff, N., Adam, Ch., Eisenbeiss, T., YETI Team
- Transit timing variation and activity in the WASP-10 planetary system 2011, MNRAS 411, 1204–1212
Maciejewski, G., Dimitrov, D., Neuhäuser, R., Tetzlaff, N., Niedzielski, A., Rätz, St., Chen, W. P., Walter, F., Marka, C., Baar, S., Krejcová, T., Budaj, J., Krushevska, V., Tachihara, K., Takahashi, H., Mugrauer, M.
- Is there a compact companion orbiting the late O-type binary star HD 164816? 2012, MNRAS 427,1014
Trepl, L., Hambaryan, V. V., Pribulla, T., Tetzlaff, N., Chini, R., Neuhäuser, R., Popov, S. B., Stahl, O., Walter, F. M., Hohle, M. M.
(Siehe online unter https://doi.org/10.1111/j.1365-2966.2012.22011.x) - Tracing the evolutionary stage of Bok globules: CCS and NH3 . 2012, A&A 537, A4
Marka, C., Schreyer, K., Launhardt, R., Semenov, D. A., Henning, Th.
(Siehe online unter https://doi.org/10.1051/0004-6361/201014375) - Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin. 2013, A&A 551, A108
Maciejewski, G., Dimitrov, D., Seeliger, M., Raetz, St., Bukowiecki, L., Kitze, M., Errmann, R., Nowak, G., Niedzielski, A., Popov, V., Marka, C., Gozdziewski, K., Neuhaeuser, R., Ohlert, J., Hinse, T. C., Lee, J. W., Lee, C.-U., Yoon, J.-N., Berndt, A., Gilbert, H., Ginski, Ch., Hohle, M. M., Mugrauer, M., Roell, T., Schmidt, T. O. B., Tetzlaff, N., Mancini, L., Southworth, J., Dall’Ora, M., Ciceri, S., Zambelli, R., Corfini, G., Takahashi, H., Tachihara, K., Benko, J. M., Sarneczky, K., Szabo, Gy. M., Varga, T. N., Vanko, M., Joshi, Y. C., Chen, W. P.
(Siehe online unter https://doi.org/10.1051/0004-6361/201220739) - Investigation of a transiting planet candidate in Trumpler 37: An astrophysical false positive eclipsing spectroscopic binary star. 2014, AN 335, 345
Errmann, R., Torres, G., Schmidt, T. O. B., Seeliger, M., Howard, A. W., Maciejewski, G., Neuhäuser, R., Meibom, S., Kellerer, A., Dimitrov, D. P., Dincel, B., Marka, C., Mugrauer, M., Ginski, Ch., Adam, Ch., Raetz, St., Schmidt, J. G., Hohle, M. M., Berndt, A., Kitze, M., Trepl, L., Moualla, M., Eisenbeiß, T., Fiedler, S., Dathe, A., Graefe, Ch., Pawellek, N., Schreyer, K., Kjurkchieva, D. P., Radeva, V. S., et al.
(Siehe online unter https://doi.org/10.1002/asna.201412047) - The close environment of AFGL 490 in radio-interferometric observations. 2014, PhD thesis, University Jena
Marka, C.
