A 1.3 mm SMA survey of 29 variable young stellar objects

Abstract

Context. Young stellar objects (YSOs) may undergo periods of active accretion (outbursts), during which the protostellar accretion rate is temporarily enhanced by a few orders of magnitude. Whether or not these accretion outburst YSOs possess similar dust/gas reservoirs to each other, and whether or not their dust/gas reservoirs are similar as quiescent YSOs, are issues not yet clarified. Aims. The aim of this work is to characterize the millimeter thermal dust emission properties of a statistically significant sample of long and short duration accretion outburst YSOs (i.e., FUors and EXors) and the spectroscopically identified candidates of accretion outbursting YSOs (i.e., FUor-like objects). Methods. We have carried out extensive Submillimeter Array (SMA) observations mostly at ∼225 GHz (1.33 mm) and ∼272 GHz (1.10 mm), from 2008 to 2017. We covered accretion outburst YSOs located at <1 kpc distances from the solar system. Results. We analyze all the existing SMA data of such objects, both published and unpublished, in a coherent way to present a millimeter interferometric database of 29 objects. We obtained 21 detections at >3-σ significance. Detected sources except for the two cases of V883 Ori and NGC 2071 MM3 were observed with ∼1 ′′ angular resolution. Overall our observed targets show a systematically higher millimeter luminosity distribution than those of the M * >0.3 M⊙ Class II YSOs in the nearby ( 400 pc) low-mass star-forming molecular clouds (e.g., Taurus, Lupus, Upp Scorpio, and Chameleon I). In addition, at 1 mm our observed confirmed binaries or triple-system sources are systematically fainter than the rest of the sources even though their 1 mm fluxes are broadly distributed. We may have detected ∼30-60% millimeter flux variability from V2494 Cyg and V2495 Cyg, from the observations separated by ∼1 year. Conclusions. 1 Hauyu Baobab Liu et al.: SMA survey towards FU Orionis objects and EXors Fig. 1. SMA images of the observed FUors, EXors, and FUor-like objects. Images are taken at the mean frequency of 224-225 GHz (1.33 mm) if not specifically annotated. Synthesized beam is shown in the bottom left corner of each panel. Color bars are in units of mJy beam −1 . Contours are in steps of 3-σ (c.f. Table 1) if not specifically mentioned. Contours of L1551 IRS 5 are 6 mJy beam −1 (2σ) × [-3, 3, 6, 12, 24, 48]. Contours of Haro 5a/6a IRS are 2.4 mJy beam −1 (1σ) × [-3, 3, 6, 12, 24, 48]. Contours of V883 Ori are 7.6 mJy beam −1 (1σ) × [-3, 3, 6, 12, 24, 48]. Contours of V2775 Ori are 1.9 mJy beam −1 (1σ) × [-3, 3, 6, 12, 24]. Contours of V1647 Ori are 0.66 mJy beam −1 (1σ) × [-3, 3, 6, 12, 24, 48, 96]. Image of NGC 2071 MM3 is presented with a θ maj × θ min =5. ′′ 8×3. ′′ 6 (P.A.=43 • ) synthesized beam to better present its extended envelope; contours are 0.66 mJy beam −1 (1σ) × [-3, 3, 6, 12, 24, 48]. Rectangle and cross in the panel of RNO 1B/1C mark the locations of RNO 1B and 1C quoted from Quanz et al. (2007a); in the panel of SVS 13 they mark Per-emb-44 A and B (Anglada et al. 2004); in the pa...

On the Effects of Self-obscuration in the (Sub)Millimeter Spectral Indices and the Appearance of Protostellar Disks

“…Spectral indices < 2 have indeed been reported several times in the literature (Jørgensen et al 2009;Miotello et al 2014;Li et al 2017;Liu et al 2018). Sometimes they have been attributed to calibration errors, very low dust temperatures (e.g., Hirano & Liu 2014), or a significant contribution of free-free emission .…”

“…However, it is not clear to which extent selfscattering can dominate over magnetic-field alignment in the polarized emission (e.g., Lee et al 2018;Girart et al 2018). It is possible that in class 0 and I protostars magnetic fields tend to dominate (Alves et al 2018;Liu et al 2018). We conclude that self-obscuration due to relatively high masses and temperature structure could be an important part of the puzzle, helping to explain low spectral indices without needing to invoke significant dust evolution at the earliest YSO stages.…”

Diagnosing 0.1–10 au Scale Morphology of the FU Ori Disk Using ALMA and VLTI/GRAVITY

“…Moreover, this explains how the 0.1-0.3 au scale hot inner disk with a 10 −4 M e yr −1 mass accretion rate (see Section 4.1) is being replenished by the up to ∼10 au scale gas reservoir at a modest rate, such that the hot inner disk neither becomes depleted nor accumulates mass over a short timescale. This may explain the relatively stable mid-infrared and (sub) millimeter fluxes in the previous monitoring observations (Green et al 2016a;Liu et al 2018).…”

Disks around FUor-type young eruptive stars with ALMA

“…The outbursts clear the material surrounding the star, helping the transition from the embedded Class I to disk-only Class II. Recent studies have shown that FUor disks are smaller and more massive than previously thought (Cieza et al 2018, andLiu et al 2018).…”