Abstract
Herbig Ae/Be stars are intermediate-mass pre-main sequence stars undergoing accretion through their circumstellar disk. The optical and infrared (IR) spectra of HAeBe stars show Hi emission lines belonging to Balmer, Paschen and Brackett series. We used the archival X-Shooter spectra available for 109 HAeBe stars from Vioque et al. (2018) and analysed the various Hi lines present in them. We segregated the stars into different classes based on the presence of higher-order lines in different Hi series. We discussed the dependence of the appearance of higher-order lines on the stellar parameters. We found that most massive and younger stars show all the higher-order lines in emission. The stars showing only lower-order lines have \(T_\textrm{eff} < {12{,}000}\) K and an age range of 5–10 Myr. We performed a case B line ratio analysis for a sub-sample of stars showing most of the Hi lines in emission. We noted that all but four stars belonging to the sub-sample show lower Hi line ratios than theoretical values, owing to the emitting medium being optically thick. The Hi line flux ratios do not depend on the star’s spectral type. Further, from the line ratios of lower-order lines and Paschen higher-order lines, we note that line ratios of most HAeBe stars match with electron density value in the range of \(10^9\)–\(10^{11}\) cm\(^{-3}\). The electron temperature, however, could not be ascertained with confidence using the line ratios studied in this work.
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Notes
\(n_e\) given in cm\(^{-3}\) units.
Pa‘n’ denotes the transition between upper-level n and the lower level corresponding to Paschen series. Similar convention is followed for Brackett series
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Acknowledgements
We thank the Science & Engineering Research Board (SERB), a statutory body of the Department of Science & Technology (DST), Government of India, for funding our research under grant number CRG/2019/005380. RA acknowledges the financial support from SERB POWER fellowship grants SPF/2020/000009. We are grateful to the Centre for Research, CHRIST (Deemed to be University), Bangalore, for the research grant extended to carry out the current project (MRPDSC-1932). We thank the SIMBAD database and the online VizieR library service for hel** us with the literature survey and obtaining relevant data. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular, the institutions participating in the Gaia multilateral agreement.
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This article is part of the Special Issue on “Star formation studies in the context of NIR instruments on 3.6m DOT”.
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Shridharan, B., Mathew, B., Arun, R. et al. Hi line analysis of Herbig Ae/Be stars using X-Shooter spectra. J Astrophys Astron 44, 62 (2023). https://doi.org/10.1007/s12036-023-09952-w
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DOI: https://doi.org/10.1007/s12036-023-09952-w