VLT near- to mid-IR imaging and spectroscopy of the M 17 UC1 – IRS5 region

Abstract

Aims. We investigate the surroundings of the hypercompact H ii region M 17 UC1 to probe the physical properties of the associated young stellar objects and the environment of massive star formation. Methods. We use diffraction-limited near-IR (VLT/NACO) and mid-IR (VLT/VISIR) images to reveal the different morphologies at various wavelengths. Likewise, we investigate the stellar and nebular content of the region with VLT/SINFONI integral field spectroscopy with a resolution R ∼ 1500 at H + K bands. Results. Five of the seven point sources in this region show L-band excess emission. A geometric match is found between the H 2 emission and near-IR polarized light in the vicinity of IRS5A, and between the diffuse mid-IR emission and near-IR polarization north of UC1. The H 2 emission is typical for dense photodissociation regions (PDRs), which are initially far-ultraviolet pumped and repopulated by collisional de-excitation. The spectral types of IRS5A and B273A are B3−B7 V/III and G4−G5 III, respectively. The observed infrared luminosity L IR in the range 1−20 μm is derived for three objects; we obtain 2.0 × 10 3 L for IRS5A, 13 L for IRS5C, and 10 L for B273A. Conclusions. IRS5 might be a young quadruple system. Its primary star IRS5A is confirmed to be a high-mass protostellar object (∼9 M , ∼1 × 10 5 yrs); it might have terminated accretion due to the feedback from stellar activities (radiation pressure, outflow) and the expanding H ii region of M 17. The object UC1 might also have terminated accretion because of the expanding hypercompact H ii region, which it ionizes. The disk clearing process of the low-mass young stellar objects in this region might be accelerated by the expanding H ii region. The outflows driven by UC1 are running south-north with its northeastern side suppressed by the expanding ionization front of M 17; the blue-shifted outflow lobe of IRS5A is seen in two types of tracers along the same line of sight in the form of H 2 emission filament and mid-emission. The H 2 line ratios probe the properties of M 17 SW PDR, which is confirmed to have a clumpy structure with two temperature distributions: warm, dense molecular clumps with n H > 10 5 cm −3 and T ≈ 575 K and cooler atomic gas with n H ∼ 3.7 × 10 3 −1.5 × 10 4 cm −3 and T ∼ 50−200 K.

TIC 278956474: Two Close Binaries in One Young Quadruple System Identified by TESS

“…Known young quadruple systems include GG Tauri (Guilloteau et al 1999;Köhler 2011), HD 98800 (Tokovinin 1999;Ribas et al 2018), HD 34700 (Sterzik et al 2005), AB Doradus (Janson et al 2007;Wolter et al 2014), AO Vel (González et al 2006(González et al , 2008b, HD 91962 (Tokovinin et al 2015), LkCa 3 (Torres et al 2013; Baraffe et al 2015) and HD 86588 (Tokovinin et al 2018). IRS5 might be a young quadruple system (Chen et al 2015). LkHα 263C, around which a circumstellar disc has been identified (Jayawardhana et al 2002), appears to be a member of a young quadruple system in the MBM 12 association.…”

Massive pre-main-sequence stars in M17

“…Once the accretion rate diminishes, the so-called bloated pre-main-sequence (PMS) star contracts to the main sequence on the Kelvin-Helmholtz timescale. Recently, candidates for such bloated, massive PMS stars have been spectroscopically confirmed (Ochsendorf et al 2011;Bik et al 2012;Ellerbroek et al 2013a;Chen et al 2015).…”

“…NGC 6618 is a young cluster, whose age is estimated at about 1 Myr (Hanson et al 1997, hereafter H97;Broos et al 2007;Povich et al 2009), while the surrounding molecular cloud hosts PMS stars. The photodissociation region to the southwest of NGC 6618 includes several candidate mYSOs: the hyper-compact H ii region M17-UC1 surrounded by a circumstellar disk (Nielbock et al 2007), and IRS5, a young possibly quadruple system of which the primary star, IRS5A (B3-B7 V/III), is a high-mass protostellar object (∼9 M , ∼10 5 yr; Chen et al 2015). H97 discovered a sample of highmass (5-20 M ) YSOs in the same area.…”

Massive pre-main sequence stars in M17

“…Once the accretion rate diminishes, the "bloated" pre-main-sequence (PMS) star contracts to the main sequence on the Kelvin-Helmholtz timescale. Recently, candidates for such bloated, massive PMS stars have been spectroscopically confirmed (Ochsendorf et al 2011;Bik et al 2012;Ellerbroek et al 2013a;Chen et al 2015).…”

“…NGC 6618 is a young cluster, its age is estimated at about 1 Myr (Hanson et al 1997;Broos et al 2007;Povich et al 2009), while the surrounding molecular cloud hosts pre-main-sequence stars. The photodissociation region to the southwest of NGC 6618 includes several candidate mYSOs: the hyper-compact H ii region M17-UC1 surrounded by a circumstellar disk (Nielbock et al 2007), and IRS5, a young possibly quadruple system of which the primary star, IRS5A (B3-B7 V/III), is a high-mass protostellar object (∼9 M , ∼ 10 5 yr, Chen et al 2015). Hanson et al (1997) (hereafter H97) discovered a sample of high-mass (5-20 M ) young stellar objects in the same area.…”