SimultaneousChandraand Very Large Array Observations of Young Stars and Protostars in ρ Ophiuchus Cloud Core A

Abstract

A 96 ks Chandra X-ray observation of Ophiuchus cloud core A detected 87 sources, of which 60 were identified with counterparts at other wavelengths. The X-ray detections include 12 of 14 known classical T Tauri stars (CTTSs) in the field, 15 of 17 known weak-lined TTSs ( WTTSs), and 4 of 15 brown dwarf candidates. The X-ray detections are characterized by hard, heavily absorbed emission. Most X-ray detections have visual extinctions in the range A V % 10 20 mag, but several sources with visual absorptions as high as A V % 40 56 mag were detected. The mean photon energy of a typical source is hEi % 3 keV, and more than half of the detections are variable. Prominent X-ray flares were detected in the unusual close binary system Oph S1, the X-ray-bright WTTS DoAr 21, and the brown dwarf candidate GY 31 ( M5.5). Time-resolved spectroscopic analysis of the DoAr 21 flare clearly reveals a sequence of secondary flares during the decay phase that may have reheated the plasma. We find that the X-ray luminosity distributions and spectral hardnesses of CTTSs and WTTSs are similar. We also conclude that the X-ray emission of detected brown dwarf candidates is less luminous than TTSs, but spectroscopically similar. Simultaneous multifrequency Very Large Array ( VLA) observations detected 31 radio sources at 6 cm, of which 10 were also detected by Chandra. We report new radio detections of the optically invisible IR source WLY 2-11 and the faint H emission line star Elias 24 (class II ). We confirm circular polarization in Oph S1 and report a new detection of circular polarization in DoAr 21. We find no evidence that X-ray and radio luminosities are correlated in the small sample of TTSs detected simultaneously with Chandra and the VLA. We describe a new nonparametric method for estimating X-ray spectral properties from unbinned photon event lists that is applicable to both faint and bright X-ray sources. The method is used to generate f X , log T , and L X light curves. In addition, we provide a publicly available electronic database containing multiwavelength data for 345 known X-ray, IR, and radio sources in the core A region.

First stars of theρOphiuchi dark cloud

“…One protostar/Class I object is at the very edge of XMM-Newton FOV and it is undetected, another Class I object is Haro 1-4 which is detected. In contrast, L1688 core contains a significant number of stars with disks and protostars embedded in the densest part of the cloud (Gagné et al 2004), and the ratio stars with disks to disk-less stars is of order of one or more. The age inferred from the ratio disks/no-disk objects around ρ Ophiuchi is about 5 Myr, while for the YSOs embedded in L1688 an age t < 1 Myr is inferred (Luhman & Rieke 1999;Natta et al 2002).…”

“…The uncertainty on the distance can produce a systematic error of the X-ray luminosities of ∼0.16 dex. The main core of the cloud, L1688, contains high density gas and dust and a stellar population of about 300 young stellar objects (YSOs, Gagné et al 2004;Wilking et al 2005). The dense core F of the cloud has been extensively studied in infrared and X-rays.…”

“…The dense core F of the cloud has been extensively studied in infrared and X-rays. In X-rays, several Chandra observations have targeted L1688 for a total duration of about 400 ks (Imanishi et al 2001;Gagné et al 2004). XMM-Newton has also observed L1688 with a 35 ks exposure (Ozawa et al 2005), and with a large program named DROXO (PI: S. Sciortino, exposure ∼500 ks) aimed at obtaining a deep observation to characterize the X-rays properties of the YSOs embedded in the L1688 core (Giardino et al 2007;Flaccomio et al 2009;Pillitteri et al 2010).…”

Spectroscopy of new brown dwarf members ofρ Ophiuchi and an updated initial mass function

“…They combined all the new members with 88 previously known members with optical spectral type from an analogous optical survey (Wilking et al 2005), 14 members compiled from the literature, and three members for which they presented optical spectral types but had already near-IR spectral types determined by Luhman & Rieke (1999); -in this work we confirm spectroscopically three new members with spectral types indicative of masses above the substellar limit (besides the 13 brown dwarfs already included in Table 5, and the four members with uncertain spectral types that we do not include in this analysis); totalling a list of 250 members of the cluster where 208 have spectral types earlier than M6, and 42 have spectral types later than or equal to M6. Several other sources have been associated with the cloud through X-rays (Imanishi et al 2001;Gagné et al 2004;Ozawa et al 2005;Pillitteri et al 2010), near-IR variability (Alves de Oliveira et al 2010), mid-IR excess (Padgett et al 2008;Wilking et al 2008;Gutermuth et al 2009;Marsh et al 2010), and methane photometric colours (Haisch et al 2010), but lack spectroscopic confirmation. X-ray surveys have low contamination A151, page 12 of 17 rates, particularly when large amounts of extinction block background contaminants, though at faint magnitudes, extragalactic contamination is present.…”

X-Shooter study of accretion inρ-Ophiucus: very low-mass stars and brown dwarfs

“…The total population of the surrounding Ophiucus region is estimated to be of around 300 YSOs , with ∼200 YSOs located in ρ-Oph itself. Given the large quantity of YSOs present in this cluster and its proximity, it has been extensively studied in the past at various wavelengths from optical, near-and far-infrared, millimeter, radio, to X-ray (e.g., Greene & Meyer 1995;Luhman & Rieke 1999;Wilking et al 2005;Alves de Oliveira et al 2010, 2012Bontemps et al 2001;McClure et al 2010;Gagné et al 2004).…”