scholarly journals A Highly-collimated Water Maser Bipolar Outflow in the Cepheus A HW3d Massive Protostellar Object

2012 ◽  
Vol 8 (S287) ◽  
pp. 141-145
Author(s):  
James O. Chibueze ◽  
Hiroshi Imai ◽  
Daniel Tafoya ◽  
Toshihiro Omodaka ◽  
Osamu Kameya ◽  
...  
Keyword(s):  
Strong Support ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Very Large Array ◽  
Star Forming ◽  
Bipolar Outflow ◽  
Long Baseline ◽  
Cepheus A ◽  
Continuum Data ◽  
Water Maser

AbstractWe report the results of multi-epoch very long baseline interferometry (VLBI) water (H2O) maser observations carried out with the VLBI Exploration of Radio Astrometry (VERA) toward the HW3d object within the Cepheus A star-forming region. We measured proper motions of 30 water maser features, tracing a compact bipolar outflow. This outflow is highly collimated, extending through ~400 mas (290 AU), and having a typical proper motion velocity of ~6 mas yr−1 (~21 km s−1). The dynamical timescale of the outflow was estimated to be ~100 years, showing that the outflow is tracing a very early star-formation phase. Our results provide strong support that the HW3d object harbors an internal massive protostar, as previous observations suggested. In addition, we have analyzed Very Large Array (VLA) archive 1.3 cm continuum data of the 1995 and 2006 epochs obtained towards Cepheus A. These results indicate possible different protostars around HW3d and/or strong variability in its radio continuum emission.

scholarly journals Observations of H2O maser and continuum emission in AFGL 2591

2002 ◽  
Vol 206 ◽  
pp. 68-71
Author(s):  
Miguel A. Trinidad ◽  
Salvador Curiel ◽  
Jorge Cantó ◽  
José M. Torrelles ◽  
Luis F. Rodríguez ◽  
...  
Keyword(s):  
Radio Continuum ◽  
Continuum Emission ◽  
Molecular Flow ◽  
Large Array ◽  
Very Large Array ◽  
Star Forming ◽  
Bipolar Outflow ◽  
Maser Line ◽  
H Ii Region

We report results of radio continuum (1.3 and 3.6 cm) and H2O maser line observations, made with the Very Large Array (A configuration), toward the star-forming region AFGL 2591. We detected 85 maser spots toward this region, which are distributed in three main groups. Two of these groups spatially coincide with the radio continuum sources VLA 2 and VLA 3. The maser spots associated with VLA 3 are distributed along a shell-like structure of 0.01 and nearly perpendicular to the CO bipolar outflow. We propose that VLA 3 is the center of the observed molecular flow in this region. Finally, we confirm that AFGL 2591 region is a cluster of B type stars, each one with its own optically thin H II region.

scholarly journals Characterizing the radio continuum nature of sources in the massive star-forming region W75N (B)

2020 ◽  
Vol 496 (3) ◽  
pp. 3128-3141 ◽  
Author(s):  
A Rodríguez-Kamenetzky ◽  
C Carrasco-González ◽  
J M Torrelles ◽  
W H T Vlemmings ◽  
L F Rodríguez ◽  
...  
Keyword(s):  
Massive Star ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Very Large Array ◽  
Star Forming ◽  
Thermal Radio ◽  
Wide Range ◽  
H Ii Region ◽  
Continuum Data

ABSTRACT The massive star-forming region W75N (B) is thought to host a cluster of massive protostars (VLA 1, VLA 2, and VLA 3) undergoing different evolutionary stages. In this work, we present radio continuum data with the highest sensitivity and angular resolution obtained to date in this region, using the VLA-A and covering a wide range of frequencies (4–48 GHz), which allowed us to study the morphology and the nature of the emission of the different radio continuum sources. We also performed complementary studies with multi-epoch Very Large Array (VLA) data and Atacama Large Millimeter Array (ALMA) archive data at 1.3 mm wavelength. We find that VLA 1 is driving a thermal radio jet at scales of ≈0.1 arcsec (≈130 au), but also shows signs of an incipient hypercompact H ii region at scales of ≲1 arcsec (≲1300 au). VLA 3 is also driving a thermal radio jet at scales of a few tenths of arcsec (few hundred of au). We conclude that this jet is shock exciting the radio continuum sources Bc and VLA 4 (obscured Herbig–Haro objects), which show proper motions moving outward from VLA 3 at velocities of ≈112–118 km s−1. We have also detected three new weak radio continuum sources, two of them associated with millimetre continuum cores observed with ALMA, suggesting that these two sources are also embedded young stellar objects in this massive star-forming region.

scholarly journals Protostellar Outflows at the EarliesT Stages (POETS)

2018 ◽  
Vol 619 ◽  
pp. A107 ◽  
Author(s):  
A. Sanna ◽  
L. Moscadelli ◽  
C. Goddi ◽  
V. Krishnan ◽  
F. Massi
Keyword(s):  
Spectral Index ◽  
Young Stars ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Stellar Winds ◽  
Distance Measurements ◽  
Very Large Array ◽  
Star Forming ◽  
Continuum Source ◽  
Star Forming Regions

Context. Weak and compact radio continuum and H2O masers are preferred tracers of the outflow activity nearby very young stars. Aims. We want to image the centimeter free–free continuum emission in the range 1–7 cm (26–4 GHz), which arises in the inner few 1000 au from those young stars also associated with bright H2O masers. We seek to study the radio continuum properties in combination with the H2O maser kinematics to quantify the outflow energetics powered by single young stars. Methods. We made use of the Karl G. Jansky Very Large Array (VLA) in the B configuration at K band and the A configuration at both Ku and C bands in order to image the radio continuum emission toward 25 H2O maser sites with an angular resolution and thermal rms on the order of 0.′′1 and 10 μJy beam−1, respectively. These targets add to our pilot study of 11 maser sites previously presented. The sample of H2O maser sites was selected among those regions that have accurate distance measurements, obtained through maser trigonometric parallaxes, and H2O maser luminosities in excess of 10−6 L⊙. Results. We present high-resolution radio continuum images of 33 sources belonging to 25 star-forming regions. In each region, we detect radio continuum emission within a few 1000 au of the H2O masers’ position; 50% of the radio continuum sources are associated with bolometric luminosities exceeding 5 × 103 L⊙, including W33A and G240.32 + 0.07. We provide a detailed spectral index analysis for each radio continuum source, based on the integrated fluxes at each frequency, and produce spectral index maps with the multifrequency synthesis deconvolution algorithm of CASA. The radio continuum emission traces thermal bremsstrahlung in (proto)stellar winds and jets that have flux densities at 22 GHz below 3 mJy and spectral index values between − 0.1 and 1.3. We prove a strong correlation (r > 0.8) between the radio continuum luminosity (Lrad) and the H2O maser luminosity (LH2O) of (L8 GHz∕mJy kpc2) = 103.8 × (LH2O L⊙)0.74. This power-law relation is similar to that between the radio continuum and bolometric luminosities, which confirms earlier studies. Since H2O masers are excited through shocks driven by (proto)stellar winds and jets, these results provide support to the idea that the radio continuum emission around young stars is dominated by shock ionization, and this holds over several orders of magnitude of stellar luminosites (1–105 L⊙).

The diagnostic power of radio spectra from star-forming galaxies

2019 ◽  
Vol 15 (S341) ◽  
pp. 177-186
Author(s):  
Eric J. Murphy
Keyword(s):  
Star Formation ◽  
Dust Emission ◽  
Cosmic Ray ◽  
Microwave Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Synchrotron Emission ◽  
Very Large Array ◽  
Star Forming

AbstractRadio continuum emission from galaxies is powered by a combination of distinct physical processes, each providing unique diagnostic information. Over frequencies spanning ∼ 1–120 GHz, radio spectra of star-forming galaxies are primarily comprised of: (1) non-thermal synchrotron emission powered by accelerated cosmic-ray electrons/positrons; (2) free-free emission from young massive star-forming (H ii) regions; (3) anomalous microwave emission, which is a dominant, but completely unconstrained, foreground in cosmic microwave background experiments; and (4) cold, thermal dust emission that accounts for most of the dust and total mass content in the interstellar medium in galaxies. In this proceeding, we discuss these key energetic processes that contribute to the radio emission from star-forming galaxies, with an emphasis on frequencies ≳30 GHz, where current investigations of star formation within nearby galaxies show that the free-free emission begins to dominate over non-thermal synchrotron emission. We also discuss how planned radio facilities that will access these frequencies, such as a next-generation Very Large Array (ngVLA), will be transformative to our understanding of the star formation process in galaxies.

scholarly journals High-velocity Wind from IRS 1 in the NGC 2071IR

2014 ◽  
Vol 10 (S305) ◽  
pp. 301-304
Author(s):  
Miguel Angel Trinidad
Keyword(s):  
High Velocity ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Central Source ◽  
Star Forming ◽  
The North ◽  
Infrared Sources ◽  
The Impact ◽  
Water Maser ◽  
East West

AbstractWe present the results of 1.3 and 3.6 cm radio continuum emission toward the NGC 2071IR star-forming region, carried out with the VLA in its A configuration. We detect continuum emission toward the infrared sources IRS 1 and IRS 3 at both wavelengths. In particular, IRS 1 breaks up into three continuum peaks (IRS 1E, 1C, and 1W), aligned in the east-west direction, being IRS 1 the central source. The morphology of the condensation IRS 1W is very interesting, which has an elongated structure and shows a significant curvature towards the north. We suggest that this morphology could be explained as the impact of a high-velocity wind or jetlike outflow from IRS 1 on a close companion or other obstruction, which also explains the strong water maser emission observed toward IRS 1W.

scholarly journals Radio outburst from a massive (proto)star

2018 ◽  
Vol 612 ◽  
pp. A103 ◽  
Author(s):  
R. Cesaroni ◽  
L. Moscadelli ◽  
R. Neri ◽  
A. Sanna ◽  
A. Caratti o Garatti ◽  
...  
Keyword(s):  
Flux Density ◽  
Mass Loss Rate ◽  
Strong Support ◽  
Stellar Object ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Opening Angle ◽  
Very Large Array ◽  
Young Stellar Object ◽  
Radio Outburst

Context. Recent observations of the massive young stellar object S255 NIRS 3 have revealed a large increase in both methanol maser flux density and IR emission, which have been interpreted as the result of an accretion outburst, possibly due to instabilities in a circumstellar disk. This indicates that this type of accretion event could be common in young/forming early-type stars and in their lower mass siblings, and supports the idea that accretion onto the star may occur in a non-continuous way. Aims. As accretion and ejection are believed to be tightly associated phenomena, we wanted to confirm the accretion interpretation of the outburst in S255 NIRS 3 by detecting the corresponding burst of the associated thermal jet. Methods. We monitored the radio continuum emission from S255 NIRS 3 at four bands using the Karl G. Jansky Very Large Array. The millimetre continuum emission was also observed with both the Northern Extended Millimeter Array of IRAM and the Atacama Large Millimeter/Submillimeter Array. Results. We have detected an exponential increase in the radio flux density from 6 to 45 GHz starting right after July 10, 2016, namely ~13 months after the estimated onset of the IR outburst. This is the first ever detection of a radio burst associated with an IR accretion outburst from a young stellar object. The flux density at all observed centimetre bands can be reproduced with a simple expanding jet model. At millimetre wavelengths we infer a marginal flux increase with respect to the literature values and we show this is due to free–free emission from the radio jet. Conclusions. Our model fits indicate a significant increase in the jet opening angle and ionized mass loss rate with time. For the first time, we can estimate the ionization fraction in the jet and conclude that this must be low (<14%), lending strong support to the idea that the neutral component is dominant in thermal jets. Our findings strongly suggest that recurrent accretion + ejection episodes may be the main route to the formation of massive stars.

scholarly journals Protostellar Outflows at the EarliesT Stages (POETS)

2019 ◽  
Vol 631 ◽  
pp. A74 ◽  
Author(s):  
L. Moscadelli ◽  
A. Sanna ◽  
C. Goddi ◽  
V. Krishnan ◽  
F. Massi ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Kinematic Structure ◽  
Very Large Array ◽  
Long Baseline ◽  
Independent Observations ◽  
Protostellar Outflows ◽  
Water Masers

Context. Although recent observations and theoretical simulations have pointed out that accretion disks and jets can be essential for the formation of stars with a mass of up to at least 20 M⊙, the processes regulating mass accretion and ejection are still uncertain. Aims. The goal of the Protostellar Outflows at the EarliesT Stages (POETS) survey is to image the disk-outflow interface on scales of 10–100 au in a statistically significant sample (36) of luminous young stellar objects (YSO), targeting both the molecular and ionized components of the outflows. Methods. The outflow kinematics is studied at milliarcsecond scales through very long baseline interferometry (VLBI) observations of the 22 GHz water masers, which are ideal test particles to measure the three-dimensional (3D) motion of shocks owing to the interaction of winds and jets with ambient gas. We employed the Jansky Very Large Array (JVLA) at 6, 13, and 22 GHz in the A- and B-Array configurations to determine the spatial structure and the spectral index of the radio continuum emission, and address its nature. Results. In about half of the targets, the water masers observed at separation ≤1000 au from the YSOs trace either or both of these kinematic structures: (1) a spatially elongated distribution oriented at close angle with the direction of collimation of the maser proper motions (PM), and (2) a linear local standard of rest (LSR) velocity (VLSR) gradient across the YSO position. The kinematic structure (1) is readily interpreted in terms of a protostellar jet, as confirmed in some targets via the comparison with independent observations of the YSO jets, in thermal (continuum and line) emissions, reported in the literature. The kinematic structure (2) is interpreted in terms of a disk-wind (DW) seen almost edge-on on the basis of several pieces of evidence: first, it is invariably directed perpendicular to the YSO jet; second, it agrees in orientation and polarity with the VLSR gradient in thermal emissions (when reported in the literature) identifying the YSO disk at scales of ≤1000 au; third, the PMs of the masers delineating the VLSR gradients hint at flow motions at a speed of 10–20 km s−1 directed at large angles with the disk midplane. In the remaining targets, the maser PMs are not collimated but rather tend to align along two almost perpendicular directions. To explain this peculiar PM distribution, and in light of the observational bias strongly favoring masers moving close to the plane of sky, we propose that, in these sources, the maser emission could originate in DW-jet systems slightly inclined (≤30°) with respect to edge-on. Magneto-centrifugally driven DWs could in general account for the observed velocity patterns of water masers.

The CepHeus-A Star formation and proper Motions (CHASM) Survey

2017 ◽  
Vol 13 (S336) ◽  
pp. 231-234
Author(s):  
Alberto Sanna
Keyword(s):  
Star Formation ◽  
Young Star ◽  
Young Stellar Objects ◽  
Proper Motions ◽  
Stellar Objects ◽  
Very Large Array ◽  
Star Forming ◽  
Long Baseline ◽  
T Tauri ◽  
Cepheus A

AbstractThe “CepHeus-A Star formation and proper Motions” (CHASM) survey is a large project consisting of a combination of astrometric Very Long Baseline Array (VLBA) and Jansky Very Large Array (VLA) observations, to map both the stellar and dense molecular gas components in the star-forming region Cepheus A. With the VLBA, we make use of the CH3OH and H2O maser emission in the vicinity of Cepheus A HW2, in order to measure accurate proper motions and parallax distances to both T Tauri stars and massive young stellar objects (YSOs) belonging to the same star-forming region. With the Jansky VLA, we make use of the interstellar thermometer NH3, in order to image the molecular clump surrounding Cepheus A HW2 and to determine its physical conditions. By combining these informations all together, we can provide, for instance, a direct measurement of the Bondi-Hoyle accretion radius for a massive young star, namely, HW2.

scholarly journals Protostellar Outflows at the EarliesT Stages (POETS)

2019 ◽  
Vol 623 ◽  
pp. L3 ◽  
Author(s):  
A. Sanna ◽  
L. Moscadelli ◽  
C. Goddi ◽  
M. Beltrán ◽  
C. L. Brogan ◽  
...  
Keyword(s):  
Young Star ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Relativistic Electrons ◽  
Very Large Array ◽  
Star Forming ◽  
Nonthermal Radiation ◽  
Index Analysis ◽  
Protostellar Jets ◽  
The Magnetic Field

Centimeter continuum observations of protostellar jets have revealed knots of shocked gas where the flux density decreases with frequency. This spectrum is characteristic of nonthermal synchrotron radiation and implies both magnetic fields and relativistic electrons in protostellar jets. Here, we report on one of the few detections of a nonthermal jet driven by a young massive star in the star-forming region G035.02+0.35. We made use of the NSF’s Karl G. Jansky Very Large Array (VLA) to observe this region at C, Ku, and K bands with the A- and B-array configurations, and obtained sensitive radio continuum maps down to an rms of 10 μJy beam−1. These observations allow for a detailed spectral index analysis of the radio continuum emission in the region, which we interpret as a protostellar jet with a number of knots aligned with extended 4.5 μm emission. Two knots clearly emit nonthermal radiation and are found at similar distances, of approximately 10 000 au, at each side of the central young star, from which they expand at velocities of several hundred km s−1. We estimate both the mechanical force and the magnetic field associated with the radio jet, and infer a lower limit of 0.4 × 10−4 M⊙ yr−1 km s−1 and values in the range 0.7–1.3 mG.

scholarly journals HCO+and Radio Continuum Emission from the Star Forming Region G75.78+0.34

2014 ◽  
Vol 2014 ◽  
pp. 1-5
Author(s):  
Rogemar A. Riffel ◽  
Everton Lüdke
Keyword(s):  
Massive Star ◽  
Emission Measure ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Ionized Gas ◽  
Very Large Array ◽  
Star Forming ◽  
Molecular Outflows ◽  
H Ii Region ◽  
The Continuum

We present 1.3 and 3.6 cm radio continuum images and a HCO+spectrum of the massive star forming region G75.78+0.34 obtained with the Very Large Array (VLA) and with the Berkley Illinois Maryland Association (BIMA) interferometer. Three structures were detected in the continuum emission: one associated with the well-known cometary H ɪɪ region, plus two more compact structures located at 6′′ east and at 2′′ south of cometary H ɪɪ region. Using the total flux and intensity peak we estimated an electron density of≈1.5 × 104 cm−3, an emission measure of≈6 × 107 cm−6 pc, a mass of ionized gas of≈3 M⊙, and a diameter of 0.05 pc for the cometary H ɪɪ region, being typical values for an ultracompact H ɪɪ region. The HCO+emission probably originates from the molecular outflows previously observed in HCN and CO.

Sign in / Sign up

Export Citation Format

Share Document