Extreme fragmentation and complex kinematics at the center of the L1287 cloud

Abstract

Aims. The filamentary, ∼10 pc scale infrared dark cloud L1287 located at a ∼929 pc parallax distance, is actively forming a dense cluster of low-mass young stellar objects (YSOs) at its inner ∼0.1 pc region. To help understand the origin of this low-mass YSO cluster, the present work aims at resolving the gas structures and kinematics with high angular resolution. Methods. We have performed ∼1 angular resolution (∼930 AU) observations at ∼1.3 mm wavelengths using the Submillimeter Array (SMA), which simultaneously covered the dust continuum emission, and various molecular line tracers for dense gas, warm gas, shocks, and outflows. Results. From a ∼2 resolution 1.3 mm continuum image we identified six dense cores, namely SMA1-6. Their gas masses are in the range of ∼ 0.4 − 4 M . From a ∼1 resolution 1.3 mm continuum image, we find a high fragmentation level, with 14 compact millimeter sources within 0.1 pc: SMA3 contains at least nine internal condensations; SMA5 and SMA6 are also resolved with two internal condensations. Intriguingly, one condensation in SMA3, and one condensation in SMA5, appear associated with the known accretion outburst YSOs RNO 1C and RNO 1B. The dense gas tracer DCN (3-2) traces well the dust continuum emission and shows a clear velocity gradient along the NW-SE direction centered at SMA3. There is another velocity gradient with opposite direction around the most luminous young stellar object IRAS 00338+6312. Conclusions. The fragmentation within 0.1 pc in L1287 is very high compared to other regions at the same spatial scales. The incoherent motions of dense gas flows are sometimes interpreted by being influenced by (proto)stellar feedback (e.g., outflows), which is not yet ruled out in this particular target source. On the other hand, the velocities (with respect to the systemic velocity) traced by DCN are small, and the directions of the velocity gradients traced by DCN are approximately perpendicular to those of the dominant CO outflow(s). Therefore, we alternatively hypothesize that the velocity gradients revealed by DCN trace the convergence from the 0.1 pc scales infalling motion towards the rotational motions around the more compact (∼ 0.02 pc) sources. This global molecular gas converging flow may feed the formation of the dense low-mass YSO cluster. Finally, we also found that IRAS 00338+6312 is the most likely powering source of the dominant CO outflow. A compact blue-shifted outflow from RNO 1C is also identified.

In search of infall motion in molecular clumps II: HCO+ (1–0) and HCN (1–0) observations toward a sub-sample of infall candidates

“…HCO + lines show both blue and red wings, and the integrated intensity map of the line wings shows a northeast-southwest outflow direction (as shown in Figure 5), which is consistent with the results of previous studies (e.g. Juárez et al 2019). In addition, rich maser sources have been found in this source, including OH, H 2 O, and a variety of methanol masers (6.7 GHz Class II, 44 GHz and 95 GHz Class I methanol masers; e.g.…”

VLA ammonia observations of L1287

“…LDN 1287 (hereafter L1287) is the densest part of a largescale filament (∼100 pc) shown by dust emission at 160, 250, † Deceased on September 27, 2017. 350, and 500 µm observed by Herschel (Schisano et al 2020;Juárez et al 2019, see Fig. 1), and is located at a distance of 929 +34 −33 pc (Rygl et al 2010).…”

“…L1287 contains an energetic bipolar molecular outflow with its axis in the northeast-southwest direction (Snell et al 1990;Yang et al 1991;Xu et al 2006;Fehér et al 2017;Juárez et al 2019). A very cold and luminous IRAS point source, IRAS 00338+6312, with an estimated bolometric luminosity of 760 L (Connelley et al 2007) is located toward the center of the outflow.…”

“…1. Herschel large-scale map (left) of H 2 column density (Juárez et al 2019). The large-scale filament, roughly in the southeast-northwest direction, can be clearly seen.…”

“…The embedded sources detected in the IR, millimeter, and centimeter continuum are identified in the enlarged view (right) of the small box in the central area (except RNO 1, which lies outside the small box). The black dots (•) in the right panel correspond to millimeter dust-continuum emission (Juárez et al 2019), and the plus signs (+) to mid-IR sources (Quanz et al 2007) and centimeter continuum sources (Anglada et al 1994).…”