Issue |
A&A
Volume 682, February 2024
|
|
---|---|---|
Article Number | A59 | |
Number of page(s) | 13 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202347911 | |
Published online | 02 February 2024 |
Exploring Be phenomena in OBA stars: A mid-infrared search★,★★
1
Department of Astronomy, Stockholm University, AlbaNova University Center,
Roslagstullsbacken 21,
114 21
Stockholm,
Sweden
e-mail: mingjie.jian@astro.su.se
2
Department of Astronomy, School of Science, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku,
Tokyo
113-0033,
Japan
3
Department of Astronomy, Beijing Normal University,
Beijing
100875,
PR China
Received:
8
September
2023
Accepted:
10
November
2023
As early-type stars with a rotation speed close to their critical velocity, Be stars experience an event called the Be phenomenon. The material in their equator is ejected into outside space during the Be phenomenon and forms a circumstellar disk. The mechanism triggering these events remains poorly understood, and observations of these events are limited because the duration of these events ranges from months to years. Long-term epoch photometry in the infrared bands is expected to be ideal for detecting Be phenomena because the brightness variation is larger than that in the optical, and the effect of interstellar extinction is weaker as well. We conducted a systematic search for Be phenomena among Milky Way OBA stars in the mid-infrared. We examined the brightness and colour variations of known classical Be stars using the WISE W1 and W2 photometry bands to quantify their characteristics. Subsequently, we established a set of criteria to identify similar photometric variations in a large sample of OBA stars. We found 916 OBA stars that show Be phenomena in the past 13 yr, 736 of which are newly discovered. The peak-to-peak variations in magnitude and colour were found to be correlated, indicating that a decretion disk is common. The increase in colour was observed to be strongly correlated with the emission of the Hα line, providing further evidence of the association with circumstellar disks. The brightness variation of a star with Be phenomena can be up to 1.5 mag, and the colour variations can be up to 0.4 mag. The median durations for the disk build-up and decay phases are 474 and 524 days, respectively (durations shorter than 180 days are not sampled). The search for Be phenomena in the WISE bands greatly enlarges the number of stars showing disk variation, and it enables multi-band photometry analysis of these events with the help of current and future optical photometry surveys.
Key words: stars: emission-line, Be / stars: massive / circumstellar matter / stars: rotation
Full Tables 2 and 3 are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5), or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/682/A59
The binned light curve for BeT stars and the figures similar to Figs. 11, 13 and 14 for all the BeT stars are available at https://github.com/MingjieJian/wisebet.
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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