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A Variable Nebula Associated with HBC 340 and HBC 341

ATel #7982; Lynne A. Hillenbrand (Caltech), Celia Zhang (Caltech), Rainer Spaeni (astroteamCERES), Christian Rusch (astroteamCERES), Egon Eisenring (astroteamCERES), Adam A. Miller (Caltech) on behalf of the intermediate Palomar Transient Factory Collaboration
on 2 Sep 2015; 21:08 UT
Credential Certification: Lynne Hillenbrand (lah@astro.caltech.edu)

Subjects: Variables, Young Stellar Object, Pre-Main-Sequence Star

Amateur astronomers Rainer Spaeni, Christian Rusch, and Egon Eisenring in Switzerland identified in October of 2014 that a nebular structure in NGC 1333 associated with the known young stars HBC 340 and HBC 341 had changed appearance. They reported in a personal communication to LAH that the nebula had faded relative to previous images, but that by November and December of 2014 it had returned to its previous brightness. The Palomar Transient Factory (PTF) has been observing the NGC 1333 field over several seasons in R-band and has also detected variations in the nebular morphology and brightness, as documented at http://www.astro.caltech.edu/~lah/hbc340/

HBC 340 was noted as a variable star by Herbig (1974; Lick Obs. Bull. 658; Figures 1/2). The source is located in the southwestern part of NGC1333, in the vicinity of many embedded young stars and Herbig Haro objects. It was cataloged as a bright near-infrared source by Strom, Vrba, & Strom (1976; AJ 81, 314; their #9a) who also noted a reflection nebula, and it was included in the comprehensive study of young stars by Cohen & Kuhi (1979, ApJS 41, 743; their #3 in NGC 1333) spectral typed K7e along with a companion star to the northeast, HBC 341 (star #9b in SVS76 and #4 in CK79), spectral typed M4.5. The RNO catalog of Cohen (1980; ApJ 85, 29, source #16) provided codes indicating two stars, very red, and an amorphous nebula, which is also known as GN 03.25.6 in the compilation catalog of Magakian (2003; AA 399, 141). Cohen & Schwartz (1983; ApJ 265, 877) assessed the [OI] emission observed by CK79 to indicate that the associated nebula was not coincidental passive reflection. A bright mid-infrared source was cataloged by the IRAS, Spitzer, and WISE missions. Getman et al. (2002; ApJ, 575, 354) reported x-ray detection of both young stars. For HBC 340, Winston et al. (2009, AJ, 137, 4777) determine a K7 spectral type (with Halpha, [OI] and CaII triplet emission) and a Class I spectral energy distribution while HBC 341 is an M5 (with Halpha emission) and Class II young stellar object. Both stars are highly extincted; dereddening as in Arnold et al. (2012, ApJS 201, 12) shows that HBC 340 may be more of a flat spectrum than a Class I SED.

The PTF data indicated that the southwestern source, HBC 340, which is the brighter of the pair, is also the more dramatic variable with changes of 1-2 mag on time scales of a week to several months. We suggest that processes associated with either time variable accretion on to the central star, or time variable extinction in the inner disk of HBC 340, are responsible for the observed variations in the extended nebula. We suggest a scenario similar to that of R Mon and NGC 2261, a.k.a. Hubble's Variable Nebula, in which the observed variations are "light echos" reflecting changing illumination of the circumstellar environment by the young accreting star, rather than changes in the extinction along the line of sight from the nebula to earth.

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