Serendipitous discovery of an outburst from HOPS 315

ATel #17057; Bringfried Stecklum (TLS Tautenburg)
on 28 Feb 2025; 16:32 UT
Credential Certification: Bringfried Stecklum (stecklum@tls-tautenburg.de)

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Serendipitous discovery of an outburst from HOPS 315 Upon examining the (NEO)WISE images of the region encompassing HOPS 358 (Sheehan+ 2024) with the WiseView tool (Caselden+ 2018), the variability of two adjacent sources became evident. The (NEO)WISE light curves of one of these sources, HOPS 315, provide clear evidence of an outburst. The W1 brightness has progressively increased from approximately 9.8 magnitude during the WISE epochs to 9.3 magnitude in 2020. Subsequently, it escalated to 7.8 magnitude by early 2022, representing its peak. Post-peak, the brightness has remained elevated at around 8.5 magnitude. The W2 light curve exhibits a similar pattern, although the increase is less pronounced, resulting in a blueing effect during the burst, with W1-W2 decreasing from approximately 2.2 to 1.6 magnitude.

HOPS 315, a protostar situated in NGC 2068, is classified as a Class I object (Furlan+ 2016), exhibiting a luminosity approximately three times solar (Sheehan+ 2022). Despite being in an advanced protostellar stage, it drives a significant SiO jet, characterized by multiple knots (Dutta+ 2022). If these features are attributed to pulsed accretion, their spacing suggests ejection events that occur approximately every 50 years. Consequently, it is plausible to hypothesize that the present outburst signifies another accretion burst.

The 850 micron dust continuum emission from this source has been systematically monitored by the JCMT transient survey (Herczeg+ 2017). Up to mid-2019, this emission remained stable, despite some variations observed in the infrared (Contreras Pena+ 2020). Since monitoring of the 450 micron emission started in 2020 (Mairs+ 2024), an increase in flux has been observed which is more pronounced in this band compared to the strength at 850 micron. The submillimeter rise was characterized as linear but became stronger until February 2022, the end of the observational period summarized by Mairs+ (2024). At this time, the IR brightness reached its maximum. Given the wavelength-dependent nature of the heating and cooling time scales (Contreras Pena+ 2020, Wolf+ 2024), it is anticipated that the submillimeter peak will be delayed with respect to that in the IR.

The second source, identified as HOPS 385 or IRAS 05435-0015, exhibits a consistent increase in brightness at a rate of approximately -0.06 magnitudes per year. This trend is overlaid with a periodic variability characterized by an amplitude of roughly 0.3 magnitudes and a periodicity of 4.3 years. It is prudent to investigate its submillimeter flux behavior as well.

The light curves are available from the link below. W1 and W2 bands are marked blue and red. W2 magnitudes are shifted by +2.04 (HOPS 315) and +1.43 (HOPS 385) to match the mean W1 magnitudes.

Caselden, D. et al. 2018ascl.soft06004C
Contreras Pena, C. et al. 2020MNRAS.495.3614C
Dutta, S. et al. 2022ApJ...931..130D
Furlan, E. et al. 2016ApJS..224....5F
Herczeg, G. J. et al. 2017ApJ...849...43H
Mairs, S. et al 2024ApJ...966..215M
Sheehan, P. D. et al. 2022ApJ...929...76S
Wolf, V. et al. 2024A&A...688A...8W

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