A Preliminary VLBA Distance to the Core of Ophiuchus, with an Accuracy of 4%

By L. Loinard, R. Torres, A. Mioduszewski, Luis F. Rodriguez. 2008

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The nonthermal 3.6 cm radio continuum emission from the young stars S1 and DoAr 21 in the core of Ophiuchus has been observed with the Very Long Baseline Array (VLBA) at 6 and 7 epochs, respectively, between June 2005 and August 2006. The typical separation between successive observations was 2-3 months. Thanks to the remarkably accurate astrometry delivered by the VLBA, the trajectory described by both stars on the plane of the sky could be traced very precisely, and modeled as the superposition of their trigonometric parallax and a uniform proper motion. The best fits yield distances to S1 and DoAr 21 of 116.9−6.4+7.2 and 121.9−5.3+5.8 pc, respectively. Combining these results, we estimate the mean distance to the Ophiuchus core to be 120.0−4.2+4.5 pc, a value consistent with several recent indirect determinations, but with a significantly improved accuracy of 4%. Both S1 and DoAr 21 happen to be members of tight binary systems, but our observations are not frequent enough to properly derive the corresponding orbital parameters. This could be done with additional data, however, and would result in a significantly improved accuracy on the distance determination.

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Citations in the corpus

• THE SPITZER c2d LEGACY RESULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES (2008, background): “Recent parallax observations of radio emission from young stars in Ophiuchus yield a distance of 120± 4.5 pc (Loinard et al. 2008).”
• Fundamental Parameters of the Milky Way Galaxy Based on VLBI Astrometry (2012, unknown): “…2009, (8) Hirota et al. 2008a, (9) Hirota et al. 2008b, (10) Hirota et al. 2011, (11) Honma et al. 2007, (12) Imai et al. 2007, (13) Kim et al. 2008, (14) Loinard et al. 2007, (15) Loinard et al. 2008, (16) Moellenbrock et al. 2009, (17) Moscadelli et al. 2009, (18) Moscadelli et al. 2011, (19)…”
• PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS (2009, background): “Each 1See http://cfa-www.harvard.edu/∼cqi/mircook.html. high angular resolution map covers 4′′ on a side, corresponding to 500 AU at the adopted distance of 125 pc to the Ophiuchus clouds (de Geus et al. 1989; Knude & Høg 1998; Lombardi et al. 2008; Loinard et al. 2008).”
• Microarcsecond Radio Astrometry (2013, methodology): “In the Ophiucus cloud, Loinard et al. (2008), using the VLBA, found that sources S1 and DoAr21 are at a mean distance of 120.0 ± 4.5 pc; Imai et al. (2007) using VERA found a consistent distance of 178+18−37 pc, albeit with larger uncertainty, for the H2O masers toward IRAS 16293−2422.”
• TADPOL: A 1.3 mm SURVEY OF DUST POLARIZATION IN STAR-FORMING CORES AND REGIONS (2013, background): “It is located in the southern edge of the Ophiuchus A cloud at a distance of 125 pc (Loinard et al. 2008).”
• Mapping the Shores of the Brown Dwarf Desert. I. Upper Scorpius (2007, background): “The star DoAr 21 was also found to be a binary in VLBA measurements by Loinard et al. (2008).”
• The Disk Substructures at High Angular Resolution Project (DSHARP). I. Motivation, Sample, Calibration, and Overview (2018, background): “…compact of the two configurations (C40-8, ≤ 6.8 km baselines; 50 mas resolution), based on their nominally closer distances (125 pc; de Geus et al. 1989; Loinard et al. 2008).3 Ten 3 Note that the 125 pc distance used to motivate the slightly coarser resolution for Oph targets was inappropriate.”
• VLBA DETERMINATION OF THE DISTANCE TO NEARBY STAR-FORMING REGIONS. III. HP TAU/G2 AND THE THREE-DIMENSIONAL STRUCTURE OF TAURUS (2009, methodology): “Introduction Several recent observations (e.g. Loinard et al. 2005, 2007, 2008; Torres et al. 2007; Menten et al. 2007; Xu et al. 2006) have demonstrated that multi-epoch VLBI observations can be used to measure the trigonometric parallax of nearby young starsto better than a few percent.”
• Spectroastrometric Imaging of Molecular Gas within Protoplanetary Disk Gaps (2008, background): “…TW Hya, SR 21 and HD 135344B, are part of the class of so-called “transitional” or “cold” disks, which show dust gaps or holes out to 4, 18 and 45AU, respectively (Calvet et al. 2002; Brown et al. 2007), at distances of 51, 120 and 84 pc (Mamajek 2005; Loinard et al. 2008; Sylvester et al. 1996).”
• A Keplerian disk around a Class 0 source: ALMA observations of VLA1623A (2013, background): “VLA1623 is a triple non-coeval protostellar system (Murillo & Lai 2013; Chen et al. 2013) with a prominent outflow (André et al. 1990) located in ρ Ophiuchus (d ∼ 120 pc, Loinard et al. 2008).”
• DETECTION OF THE SIMPLEST SUGAR, GLYCOLALDEHYDE, IN A SOLAR-TYPE PROTOSTAR WITH ALMA (2012, background): “The protostellar (Class 0) binary IRAS16293-2422 (IRAS16293 hereafter) at a distance of 120 pc (Loinard et al. 2008) has long been considered to be the best low-mass protostellar testbed for astrochemical studies (see, e.g., Blake et al. 1994; van Dishoeck et al.1995; Ceccarelli et al. 2000;…”
• RESOLVED IMAGES OF LARGE CAVITIES IN PROTOPLANETARY TRANSITION DISKS (2011, background): “This young star with spectral type G3 is still embedded in the L1688 dark cloud in the nearby Ophiuchus star-forming region, d ≈ 125pc (e.g., Lombardi et al. 2008; Loinard et al. 2008).”
• PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS. II. EXTENSION TO FAINTER SOURCES (2010, background): “Each high angular resolution map covers 4′′ on a side, corresponding to 500AU at the adopted distance of 125 pc to the Ophiuchus clouds (de Geus et al. 1989; Knude & Høg 1998; Lombardi et al. 2008; Loinard et al. 2008).”
• AN OPTICAL SPECTROSCOPIC STUDY OF T TAURI STARS. I. PHOTOSPHERIC PROPERTIES (2014, methodology): “When possible we rely on parallax distances: 120 pc for Ophiucus (Loinard et al. 2008), 131 pc for stars near the Lynds 1495 complex in Taurus (Torres et al. 2012), 147 pc for stars near T Tau (Loinard et al. 2007), 161 pc for the stars near the HP Tau complex in Taurus (Torres et al. 2009), 140 pc ”
• A spectroscopic survey of Herbig Ae/Be stars with X-shooter – I. Stellar parameters and accretion rates (2015, unknown): “…(ao) Drew et al. (1997), (ap) de Zeeuw et al. (1999), (aq) van Leeuwen (2007), (ar) Canto et al. (1984), (as) Hilton & Lahulla (1995), (at) Dahm & Simon (2005), (au) Shevchenko et al. (1999), (av) Avedisova (2000), (aw) Franco (1990), (ax) Preibisch & Mamajek (2008), (ay) Loinard et al. (2008).”