New insights into the near-IR spectroscopy of the young variable PV Cep
ATel #7935; D. Lorenzetti, T. Giannini, S. Antoniucci (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy), E. N.Kopatskaya, V. Larionov (Astronomical Institute of St. Petersburg University, Russia; St. Petersburg Observatory, Russia), A. A.Arkharov (St. Petersburg Observatory, Russia), A. Di Paola, B. Nisini (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy)
on 21 Aug 2015; 09:40 UT
Credential Certification: Dario Lorenzetti (dloren@mporzio.astro.it)
Subjects: Infra-Red, Star, Variables, Pre-Main-Sequence Star
During our EXor monitoring programme dubbed EXORCISM (EXOR OptiCal and Infrared Systematic Monitoring - Antoniucci et al. 2013 PPVI, Lorenzetti et al. 2007 ApJ 665, 1182), we have been observing the variable source PV Cep (ATel #1256; #1607). On 2015 June 1th (JD 2457175.5) we obtained at the AZT24 1m IR telescope (Campo Imperatore, Italy), a low-resolution (R∼250) near-IR spectrum (0.8 - 2.5 μm) of this target. The spectrum is shown in Fig. 1 using a thick black line, with other spectra (given for comparison) we obtained with the same instrumentation in different occasions. At shorter wavelengths (λ < 1.4 μm) PV Cep appears in the brightest state we have ever recorded: indeed, in the same night, photometry in the near-IR bands provided the values J = 9.69 mag, H = 8.50 mag, and K = 7.09 mag. The near-IR spectrum presents recombination lines (HI and HeI) and second overtone (2-0) and (3-1) CO emission features, whose fluxes are given in the Table below.
| Line(μm) | EW(Å) | F(10-13 erg/s/cm²) |
| Paδ(1.00) | −7 | 2.3±0.3 |
| HeI(1.08) | −11 | 4.1±0.3 |
| Paγ(1.09) | −19 | 6.9±0.3 |
| Paβ(1.28) | −58 | 23.7±0.2 |
| MgI+Br23(1.50) | −9 | 5.3±0.2 |
| Br13(1.61) | −8 | 4.4±0.2 |
| Br12(1.64) | −16 | 9.1±0.4 |
| Br11(1.68) | −20 | 11.8±0.4 |
| Br10(1.74) | −37 | 22.3±0.5 |
| Brγ(2.16) | −25 | 17.6±0.4 |
| CO2-0(2.29) | −19 | 14.6±0.4 |
| CO3-1(2.32) | −16 | 12.5±0.4 |
Beside our monitoring ( Fig. 1), a near-IR spectrum of PV Cep appeared in the recent literature (Caratti o Garatti et al. 2013 AA 554, 66). This was obtained on 23-24 June 2012 (JD 2456101.5), when the source was in a very faint stage (J = 12.30 mag, H = 10.73 mag, and K = 8.80 mag), comparable with the minima recurrently detected during our monitoring (Lorenzetti et al. 2011 ApJ 732, 69).
By comparing the line fluxes and the spectral shape of our 2015 spectrum (presented here) with the same parameters derived from the 2012 spectrum (Caratti o Garatti et al. 2013), the following remarks can be made:
1) While brightening PV Cep has become much bluer (ΔJ = 2.6 mag, ΔH = 2.2 mag, and ΔK = 1.7 mag) as expected for both accretion- and extinction-driven fluctuations (Lorenzetti et al. 2012 ApJ 749, 188).
2) Atomic lines (HI, HeI) are now increased by a factor of 10-20; in particular, Paβ (1.28 μm) flux is higher by a factor more than 20, to be compared with a variation of the underlying continuum (J-band) by a factor 8.5 only. The same circumstance occurs also if we compare the current spectrum with the brightest one we obtained in the past (on 2004.04.01, see Fig. 1), obtaining an increase factor of 4.5 and 1.4 for line and continuum, respectively. This fact rules out the extinction as the main reason for the variation, since in that case line and underlying continuum should vary by the same amount.
3) Molecular lines in K-band (CO), whose origin is expected to be different (likely arising in the gaseous disk instead of the accretion columns), indeed present variation factors very similar (5.5 and 4.7, respectively) to that of the K-band continuum).
