Spectroscopic classification of X-ray selected stars in the rho Ophiuchi star-forming region and vicinity

Abstract

We present intermediate‐resolution (FWHM∼1.5–2.6 Å) optical spectra of 106 candidate optical counterparts of 77 X‐ray sources detected in four pointed (texp ≥ 8700 s) ROSAT PSPC observations of the ρ Ophiuchi star‐forming region and vicinity. Using the spectral types and equivalent widths of Hα and Li iλ670.8 nm obtained from our spectra, we applied spectroscopic criteria in order to classify our sample in different pre‐main‐sequence subtypes: ‘classical’ T Tauri stars (CTTS); ‘weak’ T Tauri stars (WTTS), and ‘post’ T Tauri stars (PTTS). A total of 10 CTTS, 43 WTTS and 6 PTTS were found among the PSPC‐selected stars. Our results more than double the number of pre‐main‐sequence stars spectroscopically identified in the ρ Ophiuchi region. We considered regions with different molecular cloud properties: the central core and the outer ring of the ρ Ophiuchi dark cloud (L1688); the ‘streamers’ (L1709); the R7 clump; and the ‘smoke rings’. In the inner field of L1688, the ratio of WTTS over CTTS is ∼1:1, significantly smaller than in the other regions (4:1 in the outer ring of L1688 and 5:1 in the smoke rings). The WTTS/CTTS ratio in the R7 field is the highest of our survey (10:1). We argue that this could be a result of the UV radiation from the nearby massive binary ρ Oph AB, and/or of winds from the Upper Sco OB association, which might shorten the lifetime of the circumstellar discs of the low‐mass stars. We find no PTTS in the inner field of our L1688 PSPC image, and only 3 PTTS in the outer ring despite the high sensitivity of our X‐ray observations in this region. This result confirms that the central region of L1688 is extremely young (age < 5 Myr), as suggested by near‐infrared surveys. The presence of a small number of PTTS scattered around the ρ Ophiuchi molecular clouds suggests that star formation may have been going on for 10 to 30 Myr, very slowly at first, but at a much higher rate for the last ∼10 Myr. We provide rough estimates of the star formation rate for the main ρ Ophiuchi molecular cloud complex.

The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs

“…In Oph, all our low-mass objects lie within a $35 0 ; 35 0 area of the dark core originally studied by Casanova et al (1995). We select K0-M4 stars in this region from Bouvier & Appenzeller (1992) and Martín et al (1998). For Taurus, we select stars from Briceño et al (2002) and Luhman et al (2003a) (since most of our Taurus low-mass objects lie in the Taurus fields analyzed in these two studies).…”

“…Finally, for Upper Sco we select stars from the studies by Walter et al (1994) and Preibisch et al (1998Preibisch et al ( , 2002, which together provide the most complete list of stars with available H data in this cluster to date. We have then compiled H equivalent widths for all these stars from various sources in the literature (mostly low resolution, but high resolution in a handful of cases where low-resolution data are unavailable; Oph, Bouvier & Appenzeller 1992;Martín et al 1998;Taurus, Hartmann et al 1991;Hartigan et al 1994;Martín et al 1994;Mathieu 1994;Kenyon et al 1998;Monin et al 1998;Briceño et al 1998Briceño et al , 1999White & Hillenbrand 2004;IC 348, Luhman et al 2003b;Cha I, Luhman 2004;Upper Sco, Walter et al 1994;Preibisch et al 1998Preibisch et al , 2002 and applied the BM03 accretion criteria.…”

Cold Disks: Spitzer Spectroscopy of Disks around Young Stars with Large Gaps

“…]Different dividing lines between nonaccreting weak-line T Tauri (WTT) stars and classical T Tauri (CTT) stars have been proposed, but it makes little difference to the classifications in these cases. SR 21 (0.54 in absorption:Martin et al 1998) and T Cha (2-A 10 :Gregorio-Hetem et al 1992; Alcala et al 1995) are nominallẙ A WTT stars, although T Cha is highly variable and close to the cutoff.LkHa 330 (11-20 : Fernandez et al 1995;Cohen & Kuhi 1979) A and HD 135344 (17.4 :Acke et al 2005) are clearly CTT stars. A 4.…”

c2dSpitzerIRS Spectra of Disks around T Tauri Stars. I. Silicate Emission and Grain Growth

“…Levreault 1988; (2)Cohen & Kuhi 1979; (3)Fernandez et al 1995; (4) Hartigan et al 1994; (5) D'Alessio et al 2005; (6) Kenyon et al 1998; (7) Reipurth & Pettersson 1993; (8) Sahu & Sahu 1992; (9) Lawson et al 1996; (10) Hartmann et al 1998; (11) Appenzeller et al 1983; (12) Reipurth et al 1996; (13) Saffe et al 2003; (14) Hartigan 1993; (15) van den Ancker et al 1998; (16) Alcala et al 1995; (17) Gregorio-Hetem et al 1992; (18) Sartori et al 2003; (19) Hughes & Hartigan 1992; (20) Hughes et al 1994; (21) Heyer & Graham 1989; (22) Prato et al 2003; (23) Bouvier & Appenzeller 1992; (24) Luhman & Rieke 1999;(25)Martin et al 1998; (26) Rydgren 1980; (27) Gomez de Castro 1997; (28) Natta et al 1997; (29) Finkenzeller & Mundt 1984; (30) Acke et al 2005; (31)The et al 1994; (32) Thi et al 2001; (33) Houk 1982; (34) …”