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The SMC B-type supergiant AzV322: a g-mode pulsator with a circumstellar disc

Autor
Mennickent, R. E.
Kołaczkowski, Z.
Soszyński, Igor
Cabezas, M.
Garrido, H. E.
Data publikacji
2018
Abstrakt (EN)

We present a photometric and spectroscopic study of AzV322, an emission line object located in the Small Magellanic Cloud previously classified between O9 and B0. We analyse 17.5 yr of I- and V-band OGLE-II, -III and -IV light curves and find four significant frequencies, viz. f<SUB>1</SUB> = 0.386 549 ± 0.000 003, f<SUB>2</SUB> = 0.101 177 ± 0.000 005, f<SUB>3</SUB> = 0.487 726 ± 0.000 015 and f<SUB>4</SUB> = 0.874 302 ± 0.000 020 cycles d<SUP>-1</SUP> . The f<SUB>1</SUB> frequency (period 2.587 00 ± 0.000 02 d) provides the stronger periodogram peak and gives a single wave light curve of full amplitude 0.066 mag in the I band. High-resolution optical spectroscopy confirms the early B-type spectral type and reveals prominent double peak Balmer, Paschen, O I 8446 and He I 5875 emissions. The spectral energy distribution shows significant colour excess towards long wavelengths possibly attributed to free-free emission in a disc -like envelope. Our analysis yields T<SUB>eff</SUB> = 23 000 ± 1500 K, log g = 3.0 ± 0.5, M = 16 ± 1 M<SUB>⊙</SUB>, R = 31.0 ± 1.1 R<SUB>⊙</SUB> and L<SUB>bol</SUB> = 10<SUP>4.87 ± 0.06</SUP> L<SUB>⊙</SUB>. AzV322 might be a member of the new class of slowly pulsating B supergiants introduced by Saio et al. and documented by Lefever, Puls & Aerts; however its circumstellar disc makes it an hither to unique object. Furthermore, we notice that an O-C analysis for f<SUB>1</SUB> reveals quasi-cyclic changes for the times of maximum in a time-scale of 20 yr, which might indicate a light-travel time effect in a very wide orbit binary with an undetected stellar component.

Dyscyplina PBN
astronomia
Czasopismo
Monthly Notices of the Royal Astronomical Society
Tom
473
Zeszyt
3
Strony od-do
4055-4063
ISSN
0035-8711
Data udostępnienia w otwartym dostępie
2017-10-06
Licencja otwartego dostępu
Inna