First X-ray detection of the young variable V1180 Cassiopeiae

¹ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
e-mail: simone.antoniucci@oa-roma.inaf.it
² Department of Mathematics and Physics E. De Giorgi, University of Salento, via per Arnesano, CP 193, 73100 Lecce, Italy
³ INFN, Sez. di Lecce, via per Arnesano, CP 193, 73100 Lecce, Italy
⁴ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

Received: 7 May 2015
Accepted: 4 September 2015

Abstract

Context. V1180 Cas is a young variable that has shown strong photometric fluctuations (ΔI ~ 6 mag) in the recent past, which have been attributed to events of enhanced accretion. The source has entered a new high-brightness state in September 2013, which we have previously analysed through optical and near-infrared spectroscopy.

Aims. To investigate the current active phase of V1180 Cas, we performed observations with the Chandra satellite aimed at studying the X-ray emission from the object and its connection to accretion episodes.

Methods. Chandra observations were performed in early August 2014. Complementary JHK photometry and J-band spectroscopy were taken at our Campo Imperatore facility to relate the X-ray and near-infrared emission from the target.

Results. We observe a peak of X-ray emission at the nominal position of V1180 Cas and estimate that the confidence level of the detection is about 3σ. The observed signal corresponds to an X-ray luminosity L_X(0.5−7 keV) in the range 0.8 ÷ 2.2 × 10³⁰ erg s^-1. Based on the relatively short duration of the dim states in the light curve and on stellar luminosity considerations, we explored the possibility that the brightness minima of V1180 Cas are driven by extinction variations. From the analysis of the spectral energy distribution of the high state we infer a stellar luminosity of 0.8−0.9 L_⊙ and find that the derived L_X is comparable to the average X-ray luminosity values observed in T Tauri objects. Moreover, the X-ray luminosity appears to be lower than the X-ray emission levels around 5 × 10³⁰ ÷ 1 × 10³¹ erg s^-1 detected at outbursts in similar low-mass objects.

Conclusions. Our analysis suggests that at least part of the photometric fluctuations of V1180 Cas might be extinction effects rather than the result of accretion excess emission. However, because the source displays spectral features indicative of active accretion, we speculate that its photometric variations might be the result of a combination of accretion-induced and extinction-driven effects, as suggested for other young variables, such as V1184 Tau and V2492 Cyg.