[Paper Review] Accretion in Taurus PMS binaries: a spectroscopic study

Gaspard Duchêne, Jean-Louis Monin+2 more|arXiv (Cornell University)|Sep 22, 1999

Spectroscopy and Laser Applications3 citations

TL;DR

This spectroscopic study analyzes accretion in 10 T Tauri binary systems in the Taurus star-forming region using low-resolution optical spectra to determine spectral types and Halpha equivalent widths. It finds that mixed systems (CTTS+WTTS) are rare (15–20%), and both stars in accreting binaries typically accrete simultaneously, with the more massive star showing up to 10 times higher accretion rates, indicating synchronized accretion across binary systems up to separations of 13 arcseconds.

ABSTRACT

We present low-resolution optical spectra of each component of 10 T Tauri (TT) binary systems with separations ranging from 0.9" to 3.5" and located in the Taurus star-forming region. We derive the spectral type and Halpha equivalent width of each component. Complementing these results with those of Monin et al. (1999) yields a sample of 14 binaries and one triple system, with resolved spectroscopy and/or near-infrared photometry. We find that mixed binaries (CTTS+WTTS) are rare, representing only 15-20% of the systems in the separation range of 0.8" to 3''. Supplementing these results with those of Hartigan et al. (1994) and Prato & Simon (1997), we show that the trend of binary TTS to be twins holds to separations up to 13''. This is unlikely to be the result of random pairing, and confirms previous results that both stars in young binaries accrete over the same time span. In binary systems where both stars are still accreting, our measurements show that the most massive star is usually the component with the largest accretion rate by up to a factor of 10, as determined from the Halpha luminosity.

Motivation & Objective

• To investigate accretion activity in pre-main-sequence (PMS) binary systems in the Taurus star-forming region.
• To determine whether both components of young binary systems accrete simultaneously, and if accretion rates correlate with stellar mass.
• To assess the frequency of mixed systems (Classical T Tauri stars + Weak-lined T Tauri stars) in resolved binaries.
• To extend the understanding of accretion synchronization in binaries to larger separations, up to 13 arcseconds.
• To combine spectroscopic data with existing near-infrared photometry to improve the completeness of the sample.

Proposed method

• Low-resolution optical spectroscopy was obtained for each component of 10 T Tauri binary systems in the Taurus region with separations between 0.9" and 3.5".
• Spectral types were derived from the observed spectra, and Halpha equivalent widths were measured to infer accretion activity.
• Halpha luminosity was used as a proxy for accretion rate, with higher luminosity indicating stronger accretion.
• Data were combined with prior results from Monin et al. (1999), Hartigan et al. (1994), and Prato & Simon (1997) to form a sample of 14 binaries and one triple system.
• The sample was analyzed for trends in accretion activity, spectral type similarity, and mass-accretion rate correlation across binary components.
• Statistical analysis was used to assess the significance of the observed trends, particularly the rarity of mixed systems and the correlation between mass and accretion rate.

Experimental results

Research questions

• RQ1 Are mixed binary systems (one CTTS and one WTTS) common in the Taurus region at separations up to 3.5"?
• RQ2 Do both stars in binary systems accrete over the same time span, indicating synchronized accretion?
• RQ3 Is there a correlation between stellar mass and accretion rate in binary systems where both components are accreting?
• RQ4 Does the trend of binary TTS being 'twins' in accretion activity persist at separations up to 13 arcseconds?
• RQ5 What fraction of binary systems in Taurus show evidence of ongoing accretion in both components?

Key findings

• Mixed binaries (CTTS+WTTS) are rare, comprising only 15–20% of systems in the separation range of 0.8" to 3.5".
• The majority of binary systems in Taurus show both components as either CTTS or WTTS, indicating synchronized accretion activity.
• In systems where both stars are accreting, the more massive star typically exhibits an accretion rate up to 10 times higher than its companion, as inferred from Halpha luminosity.
• The trend of binary T Tauri stars being 'twins' in accretion behavior holds up to separations of 13", suggesting that accretion is synchronized across the system.
• The rarity of mixed systems is unlikely due to random pairing, supporting the idea that accretion timescales are correlated in binary systems.
• The combined sample of 14 binaries and one triple system confirms that accretion activity is strongly correlated between components, especially at separations below 13".