Young Stellar Variability of GM Cephei by Circumstellar Dust Clumps

Po-Chieh Huang; Wen-Ping Chen; Chia-Ling Hu; Otabek Burkhonov; Shuhrat Ehgamberdiev; Jinzhong Liu; Hiroyuki Naito; Erika Pakstiene; Jan Kare Trandem Qvam; Stefanie Rätz; Evgeni Semkov; Collaboration YETY

doi:10.25518/0037-9565.7594

Bulletin de la Société Royale des Sciences de Liège

0037-9565 1783-5720

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Young Stellar Variability of GM Cephei by Circumstellar Dust Clumps

(Volume 87 - Année 2018 — Actes de colloques — First Belgo-Indian Network for Astronomy & Astrophysics (BINA) workshop - November 2016 - Nainital, India)

DOI: 10.25518/0037-9565.7594

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Mots-clés : astronomie, astrophysique, photométrie, polarimétrie, stars, variability

Abstract

UX Orionis stars are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such an UX Orionis star in the young (∼ 4 Myr) open cluster Trumpler 37 at ∼ 900 pc, showing a prominent infrared access, H-alpha emission, and flare activity. Our multi-color photometric monitoring from 2009 to 2016 showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) cyclic, but not strictly periodical, occultation events, each lasting for a couple months, with a probable recurrence time of about two years, (iii) normal dust reddening as the star became redder when dimmer, (iv) the unusual ”blueing” phenomena near the brightness minima, during which the star appeared bluer when dimmer, and (v) a noticeable polarization, from 3 to 9 percent in g’, r’, and i’ -bands. The occultation events may be caused by dust clumps, signifying the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. The level of polarization was anti-correlated with the brightness in the bright state, when the dust clump backscattered stellar light. We discussed two potential hypotheses: orbiting dust clumps versus dust clumps along a spiral arm structure.

Keywords : astronomy, astrophysics, photometry, polarimetry, stars, variability

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Po-Chieh Huang, Wen-Ping Chen, Chia-Ling Hu, Otabek Burkhonov, Shuhrat Ehgamberdiev, Jinzhong Liu, Hiroyuki Naito, Erika Pakstiene, Jan Kare Trandem Qvam, Stefanie Rätz, Evgeni Semkov & Collaboration YETY, «Young Stellar Variability of GM Cephei by Circumstellar Dust Clumps», Bulletin de la Société Royale des Sciences de Liège [En ligne], Volume 87 - Année 2018, Actes de colloques, First Belgo-Indian Network for Astronomy & Astrophysics (BINA) workshop - November 2016 - Nainital, India, 145 - 149 URL : http://popups.ulg.be/0037-9565/index.php?id=7594.