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The New EXor Outburst of ESO-H alpha 99 Observed by Gaia ATLAS and TESS
Univ Hawaii, Inst Astron, 640 N Aohoku Pl, Hilo, HI 96720 USA.
Univ Hawaii, Inst Astron, 640 N Aohoku Pl, Hilo, HI 96720 USA.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
Univ Hawaii, Inst Astron, 2680 Woodlawn Dr, Honolulu, HI 96822 USA.
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2019 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 158, no 6, article id 241Article in journal (Refereed) Published
Abstract [en]

We report photometry and spectroscopy of the outburst of the young stellar object ESO-H?99. The outburst was first noticed in Gaia alert Gaia18dvc and later by the Asteroid Terrestrial-impact Last Alert System (ATLAS). We have established the outburst light curve with archival ATLAS orange filter photometry, Gaia data, new V-band photometry, and J, H, and K-s photometry from the Infrared Imaging System (IRIS) and the United Kingdom Infrared Telescope (UKIRT). The brightness has fluctuated several times near the light curve maximum. The Transiting Exoplanet Survey Satellite (TESS) satellite observed ESO-H99 with high cadence during one of these minor minima and found brightness fluctuations on timescales of days and hours. Imaging with UKIRT shows the outline of an outflow cavity, and we find one knot of emission, now named MHO 1520, on the symmetry axis of this nebula, indicating recent collimated outflow activity from ESO-H99. Its pre-outburst SED shows a flat far-infrared spectrum, confirming its early evolutionary state and its similarity to other deeply embedded objects in the broader EXor class. The pre-outburst luminosity is 34 L, a much higher luminosity than typical EXors, indicating that ESO-H alpha 99 may be a star of intermediate mass. Infrared and optical spectroscopy show a rich emission-line spectrum, including H i lines, strong red Ca ii emission, as well as infrared CO bandhead emission, all characteristic EXors in the broadest sense. Comparison of the present spectra with an optical spectrum obtained in 1993, presumably in the quiescent state of the object, shows that during the present outburst the continuum component of the spectrum has increased notably more than the emission lines. The H alpha equivalent width during the outburst is down to one-half of its 1993 level, and shock-excited emission lines are much less prominent.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2019. Vol. 158, no 6, article id 241
Keywords [en]
Eruptive variable stars, Young stellar objects, T Tauri stars, Infrared photometry, Flash spectra, Stellar jets
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-400053DOI: 10.3847/1538-3881/ab471aISI: 000499387100001OAI: oai:DiVA.org:uu-400053DiVA, id: diva2:1380075
Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2019-12-18Bibliographically approved

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Pettersson, Bertil

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