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J/AJ/153/240  ALMA survey of protoplanetary disks in sigma Ori  (Ansdell+, 2017)

An ALMA survey of protoplanetary disks in the σ Orionis cluster. Ansdell M., Williams J.P., Manara C.F., Miotello A., Facchini S., van der Marel N., Testi L., van Dishoeck E.F. <Astron. J., 153, 240-240 (2017)> =2017AJ....153..240A (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Associations, stellar ; YSOs ; Radio lines ; Photometry, millimetric/submm ; Spectral types ; Stars, masses Keywords: accretion, accretion disks - circumstellar matter - planets and satellites: formation - protoplanetary disks - stars: pre-main sequence - stars: protostars Abstract: The σ Orionis cluster is important for studying protoplanetary disk evolution, as its intermediate age (∼3-5Myr) is comparable to the median disk lifetime. We use ALMA to conduct a high-sensitivity survey of dust and gas in 92 protoplanetary disks around σ Orionis members with M*≳0.1M. Our observations cover the 1.33mm continuum and several CO J=2-1 lines: out of 92 sources, we detect 37 in the millimeter continuum and 6 in 12CO, 3 in 13CO, and none in C18O. Using the continuum emission to estimate dust mass, we find only 11 disks with Mdust≳10M, indicating that after only a few Myr of evolution most disks lack sufficient dust to form giant planet cores. Stacking the individually undetected continuum sources limits their average dust mass to 5x lower than that of the faintest detected disk, supporting theoretical models that indicate rapid dissipation once disk clearing begins. Comparing the protoplanetary disk population in σ Orionis to those of other star-forming regions supports the steady decline in average dust mass and the steepening of the Mdust-M* relation with age; studying these evolutionary trends can inform the relative importance of different disk processes during key eras of planet formation. External photoevaporation from the central O9 star is influencing disk evolution throughout the region: dust masses clearly decline with decreasing separation from the photoionizing source, and the handful of CO detections exist at projected separations of >1.5pc. Collectively, our findings indicate that giant planet formation is inherently rare and/or well underway by a few Myr of age. Description: Our sample consists of the 92 Young Stellar Objects (YSOs) in σ Orionis with infrared excesses consistent with the presence of a protoplanetary disk. hese sources are identified by cross-matching the Class II and transition disk (TD) candidates from the Spitzer survey of Hernandez et al. 2007 (Cat. J/ApJ/662/1067) with the Mayrit catalog (Caballero 2008, Cat. J/A+A/478/667). Both catalogs are expected to be complete down to the brown dwarf limit. Disk classifications are based on the Spitzer/Infrared Array Camera (IRAC) Spectral Energy Distribution (SED) slope, as described in Hernandez et al. 2007 (Cat. J/ApJ/662/1067). We also include in our sample a Class I disk (source 1153), as it is located near the Spitzer/IRAC color cutoff for Class II disks. Our Band 6 Atacama Large Millimeter/sub-millimeter Array (ALMA) observations were obtained on 2016 July 30 and 31 during Cycle 3 (Project ID: 2015.1.00089.S; PI: Williams). The array configuration used 36 and 37 12m antennas on July 30 and 31, respectively, with baselines of 15-1124m on both runs. The correlator setup included two broadband continuum windows centered on 234.293 and 216.484GHz with bandwidths of 2.000 and 1.875GHz and channel widths of 15.625 and 0.976MHz, respectively. The bandwidth-weighted mean continuum frequency was 225.676GHz (1.33mm). The spectral windows covered the 12CO (230.538GHz), 13CO (220.399GHz), and C18O (219.560GHz) J=2-1 transitions at velocity resolutions of 0.16-0.17km/s. These spectral windows were centered on 230.531, 220.392, and 219.554GHz with bandwidths of 11.719MHz and channel widths of 0.122MHz. On-source integration times were 1.2 minutes per object for an average continuum rms of 0.15mJy/beam (Table1). This sensitivity was based on the James Clerk Maxwell Telescope (JCMT)/Submillimeter Common User Bolometer Array (SCUBA)-2 survey of σ Orionis disks by Williams et al. 2013 (Cat. J/MNRAS/435/1671), who found that stacking their individual non-detections revealed a mean 850µm continuum signal of 1.3mJy at 4σ significance. The sensitivity of our ALMA survey was therefore chosen to provide ∼3-4σ detections of such disks at 1.3mm, based on an extrapolation of the 850µm mean signal using a spectral slope of α=2-3. Table1 presents the 1.33mm continuum flux densities and associated uncertainties (F1.33mm). Table2 gives our integrated line fluxes or upper limits. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 80 92 Continuum properties table2.dat 38 92 Gas properties
See also: J/A+A/594/A85 : 2D disk models from CO isotopologues line (Miotello+, 2016) J/AJ/152/213 : Interferometry and spectroscopy of sig Ori (Schaefer+, 2016) J/ApJ/831/125 : ALMA 887um obs. of ChaI SFR (Pascucci+, 2016) J/ApJ/828/46 : ALMA survey of Lupus protoplanetary disks. (Ansdell+, 2016) J/ApJ/827/142 : ALMA observations of GKM stars in U. Sco (Barenfeld+, 2016) J/ApJ/794/36 : sig Orionis cluster stellar population (Hernandez+, 2014) J/MNRAS/435/1671 : SCUBA-2 850um survey in sig Ori cluster (Williams+, 2013) J/A+A/548/A56 : X-shooter spectra of 12 YSOs (Rigliaco+, 2012) J/A+A/478/667 : The Mayrit catalogue (Caballero, 2008) J/ApJ/662/1067 : Sptizer observations of sigma Orionis (Hernandez+, 2007) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 4 I4 --- [HHM2007] [73/1369] Source identification number (G1) 6- 7 I2 h RAh Hour of Right Ascension (J2000) (1) 9- 10 I2 min RAm Minute of Right Ascension (J2000) (1) 12- 17 F6.3 s RAs Second of Right Ascension (J2000) (1) 19 A1 --- DE- Sign of the Declination (J2000) (1) 20- 21 I2 deg DEd Degree of Declination (J2000) (1) 23- 24 I2 arcmin DEm Arcminute of Declination (J2000) (1) 26- 30 F5.2 arcsec DEs Arcsecond of Declination (J2000) (1) 32- 35 A4 --- SpT Spectral type (2) 37- 39 F3.1 --- e_SpT Uncertainty in SpT 41- 43 A3 --- r_SpT Reference for SpT (H14, R12, or VJ) (3) 45- 48 F4.2 Msun Mass [0.04/1.71] Stellar mass (M*) (4) 50- 53 F4.2 Msun e_Mass [0.01/0.32] Uncertainty in Mass (4) 55- 59 F5.2 mJy F1.33 [-0.27/15.38] Atacama Large Millimeter/sub- millimeter Array (ALMA) 1.33mm (225.676GHz) continuum emission flux density (F1.33mm) 61- 64 F4.2 mJy e_F1.33 [0.13/0.25] Uncertainty in F1.33 (5) 66- 69 F4.2 mJy/beam rms [0.13/0.18] Root-mean-square 71- 75 F5.2 Mgeo Mdust [-1.2/68.48] Dust mass (Mdust) (6) 77- 80 F4.2 Mgeo e_Mdust [0.57/1.12] Uncertainty in Mdust
Note (1): We detect only 37 out of the 92 observed sources at >3σ significance (Figure2 in the paper). For detections, the source locations are the fitted source centers output by uvmodelfit, while for non-detections they are simply the phase centers of the Atacama Large Millimeter/sub-millimeter Array (ALMA) observations, which were chosen based on 2MASS positions. The average offsets from the phase centers for the detections are Δα=0.057'' and Δδ=-0.096'' (1.9 and -3.2 pixels), both much smaller than the average beam size (Section 3 in the paper). Note (2): Spectral types were primarily taken from the homogenous sample of low-resolution optical spectra analyzed in Hernandez et al. 2014 (Cat. J/ApJ/794/36), but supplemented with those from medium-resolution VLT/X-Shooter spectra when available from Rigliaco et al. 2012 (Cat. J/A+A/548/A56). For the 23 sources that lack spectroscopic information, we estimate their spectral types using an empirical relation between V-J color and stellar spectral type; the relation was derived by measuring synthetic photometry from flux-calibrated VLT/X-Shooter spectra of Young Stellar Objects (YSOs) with spectral types from G5 to M9.5, then performing a non-parametric fit of the V-J color versus spectral type relation (Manara et al. 2017, in prep.). For these sources with photometrically derived spectral types, we cautiously assume uncertainties of ±2 spectral subtypes. We note that only 5 out of the 37 continuum detections have photometrically derived spectral types, which are less precise than the spectroscopically determined spectral types (Section 2). Note (3): Reference codes are defined as follows: H14 = Hernandez et al. 2014 (Cat. J/ApJ/794/36); R12 = Rigliaco et al. 2012 (Cat. J/A+A/548/A56); VJ = derived from V-J color indices (see Section 2). Note (4): We estimate M* values for our sample by comparing their positions on the Hertzsprung-Russel (HR) diagram to the evolutionary models of Siess et al. 2000A&A...358..593S. In order to place our targets on the HR diagram, we convert their spectral types to stellar effective temperatures (Teff) and derive their stellar luminosities (L*) from J-band magnitudes using the relations in Herczeg & Hillenbrand 2015ApJ...808...23H. The uncertainties on L* are obtained by propagating the uncertainties on spectral type and bolometric correction, and thus on distance and optical extinction (AV). We then calculate the uncertainties on M* using a Monte Carlo (MC) method, where we take the standard deviation of 1000 estimates of M*, each calculated after randomly perturbing the derived values of Teff and L* by their uncertainties. Note (5): The uncertainties are statistical errors and do not include the 10% absolute flux calibration error (Section 3 in the paper). Note (6): Our Mdust estimates, derived using Equation (1) with our F1.33mm measurements (Section 4.1): Mdust=Fνd2/KνBν(Tdust), where: Bν(Tdust) = The Planck function for a characteristic dust temperature of Tdust=20K (the median for Taurus disks; Andrews & Williams 2005ApJ...631.1134A); Kν = The dust grain opacity. We take Kν as 10cm2/g at 1000GHz and use an opacity power-law index of β=1 (Beckwith et al. 1990AJ.....99..924B); d = The source distance, taken as 385pc based on the updated parallax of the σ Ori triple system (Schaefer et al. 2016, Cat. J/AJ/152/213). Equation (1) can therefore be approximated as: Mdust≃1.34*10-5F1.33mm, where F1.33mm is in mJy and Mdust is in M.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 4 I4 --- [HHM2007] [73/1369] Source identification number (G1) 6 A1 --- l_F12CO [<] Upper limit flag on FC12O 7- 10 I4 mJy.km/s F12CO [63/1204] The 12CO (230.538GHz) line intensity (F12CO) (7) 12- 13 I2 mJy.km/s e_F12CO [33/88]? Uncertainty in F12CO (7) 15 A1 --- l_F13CO [<] Upper limit flag on F13CO 16- 18 I3 mJy.km/s F13CO [72/326] The 13CO (220.399 GHz) line intensity (F13CO) (7) 20- 21 I2 mJy.km/s e_F13CO [54/68]? Uncertainty in F13CO (7) 23 A1 --- l_FC18O [<] Upper limit flag on FC18O 24- 25 I2 mJy.km/s FC18O [48/81] The C18O (219.560GHz) line intensity (FC18O) (7) 27- 29 F3.1 MJup Mgas [2.4/7.1]? Gas mass (Mgas) 31- 33 F3.1 MJup b_Mgas [1/1]? Lower boundary (minimum mass) of Mgas (Mgas,min) 35- 38 F4.1 MJup B_Mgas [1/31.4] Upper boundary (maximum mass) of Mgas (Mgas,max)
Note (7): Of the 92 targets, only 6 are detected in 12CO, 3 are detected in 13CO, and none are detected in C18O with >4σ significance. All sources detected in 12CO are detected in the continuum, and all sources detected in 13CO are detected in 12CO.
Global Notes: Note (G1): From Hernandez, Hartmann, Megeath et al. 2007 (Cat. J/ApJ/662/1067).
History: From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 16-Aug-2017
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