scholarly journals A revised estimate of the distance to the clouds in the Chamaeleon complex using the Tycho–Gaia Astrometric Solution

2018 ◽  
Vol 610 ◽  
pp. A64 ◽  
Author(s):  
Jordan Voirin ◽  
Carlo F. Manara ◽  
Timo Prusti
Keyword(s):  
Large Scale ◽  
Galactic Plane ◽  
Stellar Content ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Systematic Uncertainties ◽  
The Galaxy ◽  
Color Excess ◽  
First Time

Context. The determination of the distance to dark star-forming clouds is a key parameter to derive the properties of the cloud itself and of its stellar content. This parameter is still loosely constrained even in nearby star-forming regions. Aim. We want to determine the distances to the clouds in the Chamaeleon-Musca complex and explore the connection between these clouds and the large-scale cloud structures in the Galaxy. Methods. We used the newly estimated distances obtained from the parallaxes measured by the Gaia satellite and included in the Tycho–Gaia Astrometric Solution catalog. When known members of a region are included in this catalog we used their distances to infer the distance to the cloud. Otherwise, we analyzed the dependence of the color excess on the distance of the stars and looked for a turn-on of this excess, which is a proxy of the position of the front-edge of the star-forming cloud. Results. We are able to measure the distance to the three Chamaeleon clouds. The distance to Chamaeleon I is 179-10-10+11+11pc, where the quoted uncertainties are statistical and systematic uncertainties, respectively, ~20 pc further away than previously assumed. The Chamaeleon II cloud is located at the distance of 181-5-10+6+11pc, which agrees with previous estimates. We are able to measure for the first time a distance to the Chamaeleon III cloud of 199-7-11+8+12pc. Finally, the distance of the Musca cloud is smaller than 603603-70-92+91+133 pc. These estimates do not allow us to distinguish between the possibility that the Chamaeleon clouds are part of a sheet of clouds parallel to the Galactic plane, or perpendicular to it. Conclusions. We measured a larger distance to the Chamaeleon I cloud than assumed in the past, confirmed the distance to the Chamaeleon II region, and measured for the first time the distance to the Chamaleon III cloud. These values are consistent with the scenario in which the three clouds are part of a single large-scale structure. Gaia Data Release 2 will allow us to put more stringent constraints on the distances to these clouds by giving us access to parallax measurements for a larger number of members of these regions.

scholarly journals The extended solar neighborhood: precision astrometry from the Pan-STARRS 1 3π Survey

2007 ◽  
Vol 3 (S248) ◽  
pp. 553-559 ◽  
Author(s):  
E. A. Magnier ◽  
M. Liu ◽  
D. G. Monet ◽  
K. C. Chambers
Keyword(s):  
Solar Neighborhood ◽  
Dynamical Structure ◽  
Nearby Star ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Low Mass ◽  
Single Epoch ◽  
Insight Into

AbstractThe Pan-STARRS pathfinding telescope PS1 will begin a major set of surveys starting in 2008, and lasting for 3.5 years. One of these, the PS1 3π Survey, will repeatedly observe the entire sky north of −30 degrees, visiting every position 12 times in each of 5 filters. With single-epoch astrometry of 10 milliarcseconds, these observations will yield parallaxes for stars within 100 pc and proper motions out to several hundred pc. The result will be an unprecedented view on nearby stellar populations and insight into the dynamical structure of the local portions of the Galaxy. One exciting science product will be a volume-limited sample of nearby low-mass objects including thousands of L dwarfs, hundreds of T dwarfs, and perhaps even cooler sub-stellar objects. Another project will use proper-motion measurements to improve the membership of nearby star forming regions.

Magnetodynamical acceleration of cosmic jets: sweeping-magnetic-twist mechanism

1986 ◽  
Vol 64 (4) ◽  
pp. 507-513 ◽  
Author(s):  
Yutaka Uchida ◽  
Kazunari Shibata
Keyword(s):  
Large Scale ◽  
Galactic Nuclei ◽  
High Energy ◽  
Point Of View ◽  
Driving Mechanism ◽  
Star Forming ◽  
Star Forming Regions ◽  
Large Scale Magnetic Field ◽  
Twisted Field ◽  
The Galaxy

Characteristic behavior of cosmic jets predicted by a magnetodynamic mechanism proposed by Uchida and Shibata is discussed in terms of recent observational results of bipolar flows from star-forming regions as examples of low-energy cases. The theoretical model considers the twisting-up of part of the large-scale magnetic field with the driving mechanism being the contracting rotation of the accretion disk around the gravitating center. The twisted field screws out the mass from the surface layers of the disk along the large-scale external field, explaining the observed tuning-fork type of distribution of the cold CO bipolar flows, gradual acceleration of the flows from the vicinity of the disk, and the helical velocity field in the outflows, all of which are not easy to explain by previous hypotheses assuming the wind and blast from the central object. Prospects of application of this mechanism to high-energy jets from active galactic nuclei or such peculiar objects in the galaxy like SS433 or Sco X-1 are discussed from the point of view of the similarity inherent in the mechanism.

scholarly journals RadioAstron space-VLBI project: studies of masers in star forming regions of our Galaxy and megamasers in external galaxies

2017 ◽  
Vol 13 (S336) ◽  
pp. 417-421 ◽  
Author(s):  
A. M. Sobolev ◽  
N. N. Shakhvorostova ◽  
A. V. Alakoz ◽  
W. A. Baan
Keyword(s):  
Angular Resolution ◽  
Nearby Galaxy ◽  
Major Step ◽  
Maser Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
External Galaxies ◽  
First Time ◽  
Water Maser

AbstractObservations of the masers in the course of RadioAstron mission yielded detections of fringes for a number of sources in both water and hydroxyl maser transitions. Several sources display numerous ultra-compact details. This proves that implementation of the space VLBI technique for maser studies is possible technically and is not always prevented by the interstellar scattering, maser beaming and other effects related to formation, transfer, and detection of the cosmic maser emission. For the first time, cosmic water maser emission was detected with projected baselines exceeding Earth Diameter. It was detected in a number of star-forming regions in the Galaxy and two megamaser galaxies NGC 4258 and NGC 3079. RadioAstron observations provided the absolute record of the angular resolution in astronomy. Fringes from the NGC 4258 megamaser were detected on baseline exceeding 25 Earth Diameters. This means that the angular resolution sufficient to measure the parallax of the water maser source in the nearby galaxy LMC was directly achieved in the cosmic maser observations. Very compact features with angular sizes about 20\muas\, have been detected in star-forming regions of our Galaxy. Corresponding linear sizes are about 5-10 million kilometers. So, the major step from milli- to micro-arcsecond resolution in maser studies is achieved by the RadioAstron mission. The existence of the features with extremely small angular sizes is established. Further implementations of the space–VLBI maser instrument for studies of the nature of cosmic objects, studies of the interaction of extremely high radiation field with molecular material and studies of the matter on the line of sight are planned.

scholarly journals The spiral potential of the Milky Way

2018 ◽  
Vol 619 ◽  
pp. A50 ◽  
Author(s):  
P. Grosbøl ◽  
G. Carraro
Keyword(s):  
Radial Velocity ◽  
Galactic Center ◽  
Galactic Plane ◽  
Small Mass ◽  
The Sun ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Best Fit ◽  
Armed Spiral

Context. The location of young sources in the Galaxy suggests a four-armed spiral structure, whereas tangential points of spiral arms observed in the integrated light at infrared and radio wavelengths indicate that only two arms are massive. Aims. Variable extinction in the Galactic plane and high light-to-mass ratios of young sources make it difficult to judge the total mass associated with the arms outlined by such tracers. The current objective is to estimate the mass associated with the Sagittarius arm by means of the kinematics of the stars across it. Methods. Spectra of 1726 candidate B- and A-type stars within 3◦ of the Galactic center (GC) were obtained with the FLAMES instrument at the VLT with a resolution of ≈6000 in the spectral range of 396–457 nm. Radial velocities were derived by least-squares fits of the spectra to synthetic ones. The final sample was limited to 1507 stars with either Gaia DR2 parallaxes or main-sequence B-type stars having reliable spectroscopic distances. Results. The solar peculiar motion in the direction of the GC relative to the local standard of rest (LSR) was estimated to U⊙ = 10.7 ± 1.3kms−1. The variation in the median radial velocity relative to the LSR as a function of distance from the sun shows a gradual increase from slightly negative values near the sun to almost 5 km s−1 at a distance of around 4 kpc. A sinusoidal function with an amplitude of 3.4 ± 1.3kms−1 and a maximum at 4.0 ± 0.6 kpc inside the sun is the best fit to the data. A positive median radial velocity relative to the LSR around 1.8 kpc, the expected distance to the Sagittarius arm, can be excluded at a 99% level of confidence. A marginal peak detected at this distance may be associated with stellar streams in the star-forming regions, but it is too narrow to be associated with a major arm feature. Conclusions. A comparison with test-particle simulations in a fixed galactic potential with an imposed spiral pattern shows the best agreement with a two-armed spiral potential having the Scutum–Crux arm as the next major inner arm. A relative radial forcing dFr ≈ 1.5% and a pattern speed in the range of 20–30 km s−1 kpc−1 yield the best fit. The lack of a positive velocity perturbation in the region around the Sagittarius arm excludes it from being a major arm. Thus, the main spiral potential of the Galaxy is two-armed, while the Sagittarius arm is an inter-arm feature with only a small mass perturbation associated with it.

scholarly journals The beauty of resolution: The SN Ib factory NGC 2770 spatially resolved

2014 ◽  
Vol 10 (S309) ◽  
pp. 169-170
Author(s):  
C. C. Thöne ◽  
L. Christensen ◽  
J. Gorosabel ◽  
A. de Ugarte Postigo
Keyword(s):  
Stellar Population ◽  
Late Type ◽  
Spiral Arms ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions ◽  
The Galaxy ◽  
History Of ◽  
First Time

AbstractThe late-type spiral NGC 2770 hosted 3 Type Ib supernovae (SNe) in or next to star-forming regions in its outer spiral arms. We study the properties of the SN sites and the galaxy at different spatial resolutions to infer propeties of the SN progenitors and the SF history of the galaxy. Several 3D techniques are used and, for the first time, we present images of metallicity, shocks and stellar population ages from OSIRIS/GTC imaging with tunable narrowband filters.

scholarly journals Micro-arcsecond astrometry with the VLBA

2007 ◽  
Vol 3 (S248) ◽  
pp. 141-147 ◽  
Author(s):  
M. J. Reid
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Proper Motions ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Trigonometric Parallaxes ◽  
Sgr A ◽  
Definition Of ◽  
Almost All

AbstractThe VLBA is now achieving parallaxes and proper motions with accuracies approaching the micro-arcsecond domain. The apparent proper motion of Sgr A*, which reflects the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0/R0 and offers a dynamical definition of the Galactic plane with Sgr A*at its origin. The intrinsic motion of Sgr A*is very small and comparable to that expected for a supermassive black hole. Trigonometric parallaxes and proper motions for a number of massive star forming regions (MSFRs) have now been measured. For almost all cases, kinematic distances exceed the true distances, suggesting that the Galactic parameters, R0 and Θ0, are inaccurate. Solutions for the Solar Motion are in general agreement with those obtained from Hipparcos data, except that MSFRs appear to be rotating slower than the Galaxy. Finally, the VLBA has been used to measure extragalactic proper motions and to map masers in distant AGN accretion disks, which will yield direct estimates of H0.

scholarly journals Star formation activity and the spatial distribution and mass segregation of dense cores in the early phases of star formation

2019 ◽  
Vol 629 ◽  
pp. A135 ◽  
Author(s):  
Sami Dib ◽  
Thomas Henning
Keyword(s):  
Spatial Distribution ◽  
Star Formation ◽  
Large Scale ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Star Formation Activity ◽  
Mass Segregation ◽  
Massive Cores

We examine the spatial distribution and mass segregation of dense molecular cloud cores in a number of nearby star forming regions (the region L1495 in Taurus, Aquila, Corona Australis, and W43) that span about four orders of magnitude in star formation activity. We used an approach based on the calculation of the minimum spanning tree, and for each region, we calculated the structure parameter 𝒬 and the mass segregation ratio ΛMSR measured for various numbers of the most massive cores. Our results indicate that the distribution of dense cores in young star forming regions is very substructured and that it is very likely that this substructure will be imprinted onto the nascent clusters that will emerge out of these clouds. With the exception of Taurus in which there is nearly no mass segregation, we observe mild-to-significant levels of mass segregation for the ensemble of the 6, 10, and 14 most massive cores in Aquila, Corona Australis, and W43, respectively. Our results suggest that the clouds’ star formation activity are linked to their structure, as traced by their population of dense cores. We also find that the fraction of massive cores that are the most mass segregated in each region correlates with the surface density of star formation in the clouds. The Taurus region with low star forming activity is associated with a highly hierarchical spatial distribution of the cores (low 𝒬 value) and the cores show no sign of being mass segregated. On the other extreme, the mini-starburst region W43-MM1 has a higher 𝒬 that is suggestive of a more centrally condensed structure. Additionally, it possesses a higher fraction of massive cores that are segregated by mass. While some limited evolutionary effects might be present, we largely attribute the correlation between the star formation activity of the clouds and their structure to a dependence on the physical conditions that have been imprinted on them by the large scale environment at the time they started to assemble.

scholarly journals Narrow-band Hα imaging of nearby Wolf–Rayet galaxies

2019 ◽  
Vol 490 (3) ◽  
pp. 3448-3453
Author(s):  
A Paswan ◽  
Kanak Saha ◽  
A Omar
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Narrow Band ◽  
Far Infrared ◽  
Infrared Excess ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Far Ultraviolet ◽  
First Time

ABSTRACT We present narrow-band Hα imaging of nearby Wolf–Rayet (WR) galaxies known as a subset of starburst galaxies. The Hα images have been used to show morphology of star-forming regions in galaxies, which leads to speculate that the studied galaxies have most likely experienced merger or interaction with low luminous dwarf galaxies or H i clouds. We further derive the Hα-based star formation rates (SFRs) in galaxies using our Hα observations. These SFRs are well correlated with SFRs derived using other indicators at far-ultraviolet, far-infrared, and 1.4-GHz radio wavebands. It is noticed that the infrared excess (IRX) method gives the best SFR estimates, consistent with different models predication. These models also predict that the sample galaxies have probably gone through a continuous star formation at least for 1 Gyr over which the recent (<10 Myr) star formation has taken place in WR phase. This study presents main-sequence (MS) relation for nearby WR galaxies for the first time. This derived MS relation is found to be similar to previously known MS relation for normal nearby star-forming galaxies, suggesting that WR systems evolve in a similar fashion as normal star-forming galaxies evolve.

scholarly journals Distances to molecular clouds at high galactic latitudes based on Gaia DR2

2019 ◽  
Vol 624 ◽  
pp. A6 ◽  
Author(s):  
Qing-Zeng Yan ◽  
Bo Zhang ◽  
Ye Xu ◽  
Sufen Guo ◽  
Jean-Pierre Macquart ◽  
...  
Keyword(s):  
Systematic Error ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Nearby Star ◽  
Bayesian Analyses ◽  
Star Forming ◽  
Star Forming Regions ◽  
Data Release ◽  
First Time ◽  
Gaia Dr2

We report the distances of molecular clouds at high Galactic latitudes (|b| > 10°) derived from parallax and G-band extinction (AG) measurements in the second Gaia data release, Gaia DR2. Aided by Bayesian analyses, we determined distances by identifying the breakpoint in the extinction AG toward molecular clouds and using the extinction AG of Gaia stars around molecular clouds to confirm the breakpoint. We used nearby star-forming regions, such as Orion, Taurus, Cepheus, and Perseus, whose distances are well known to examine the reliability of our method. By comparing with previous results, we found that the molecular cloud distances derived from this method are reliable. The systematic error in the distances is approximately 5%. In total, 52 molecular clouds have well-determined distances, most of which are at high Galactic latitudes, and we provide reliable distances for 13 molecular clouds for the first time.

scholarly journals FOREST unbiased Galactic plane imaging survey with the Nobeyama 45 m telescope (FUGIN). VI. Dense gas and mini-starbursts in the W 43 giant molecular cloud complex

2020 ◽  
Author(s):  
Mikito Kohno ◽  
Kengo Tachihara ◽  
Kazufumi Torii ◽  
Shinji Fujita ◽  
Atsushi Nishimura ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Large Scale ◽  
Galactic Plane ◽  
High Mass ◽  
Mass Star ◽  
Dense Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
Giant Molecular Cloud ◽  
Cloud Complex

Abstract We performed new large-scale 12CO, 13CO, and C18O J = 1–0 observations of the W 43 giant molecular cloud complex in the tangential direction of the Scutum arm (l ∼30°) as a part of the FUGIN project. The low-density gas traced by 12CO is distributed over 150 pc × 100 pc (l × b), and has a large velocity dispersion (20–30 km s−1). However, the dense gas traced by C18O is localized in the W 43 Main, G30.5, and W 43 South (G29.96−0.02) high-mass star-forming regions in the W 43 giant molecular cloud (GMC) complex, which have clumpy structures. We found at least two clouds with a velocity difference of ∼10–20 km s−1, both of which are likely to be physically associated with these high-mass star-forming regions based on the results of high 13CO J = 3–2 to J = 1–0 intensity ratio and morphological correspondence with the infrared dust emission. The velocity separation of these clouds in W 43 Main, G30.5, and W 43 South is too large for each cloud to be gravitationally bound. We also revealed that the dense gas in the W 43 GMC has a high local column density, while “the current SFE” (star formation efficiency) of the entire GMC is low ($\sim\!\! 4\%$) compared with the W 51 and M 17 GMC. We argue that the supersonic cloud–cloud collision hypothesis can explain the origin of the local mini-starbursts and dense gas formation in the W 43 GMC complex.

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