scholarly journals Massive stars shaping the ISM: H I holes and shells in nearby galaxies

1999 ◽  
Vol 193 ◽  
pp. 636-644
Author(s):  
Elias Brinks ◽  
Fabian Walter
Keyword(s):  
Interstellar Medium ◽  
Dwarf Galaxy ◽  
Massive Stars ◽  
Neutral Hydrogen ◽  
Neutral Medium ◽  
Stellar Winds ◽  
X Ray ◽  
Left Behind ◽  
Neutral Gas ◽  
Nearby Galaxies

Neutral hydrogen (H I) is a magnificent tool when studying the structure of the interstellar medium (ISM) as it is relatively easily observable and can be mapped at good spatial and velocity resolution with modern instruments. Moreover, it traces the cool (∼ 100 K) and warm (∼ 5000 K) neutral gas which together make up about 60%, or the bulk, of the ISM. The currently accepted picture is that stellar winds and subsequent supernovae are the origin for the clearly defined holes or bubbles within the more or less smooth neutral medium. The H I can therefore serve indirectly as a tracer of the hot interstellar medium (HIM) left behind after the most massive stars within an OB association have gone off as supernovae. A splendid example is the dwarf galaxy IC 2574 for which we discuss H I, optical and X-ray observations.

scholarly journals Search for HI Bubbles Around WR Stars: WR 149

1996 ◽  
Vol 169 ◽  
pp. 619-620
Author(s):  
C. Cappa de Nicolau ◽  
V.S. Niemela ◽  
U. Herbstmeier ◽  
B. Koribalski
Keyword(s):  
Interstellar Medium ◽  
Neutral Hydrogen ◽  
Gas Bubbles ◽  
Stellar Winds ◽  
Hydrogen Distribution ◽  
Neutral Gas ◽  
Rayet Star

The interaction of strong stellar winds with the interstellar medium creates large cavities or interstellar bubbles surrounded by expanding outer shells. 21-cm line (HI) observations have revealed the presence of such neutral gas bubbles around several WR stars (e.g. Niemela & Cappa de Nicolau 1991 and references therein; Dubner et al. 1992).Continuing our search for HI bubbles around WR stars, we have analyzed the neutral hydrogen distribution in the vicinity of the Wolf-Rayet star WR149, a highly reddened WN6-7 star located at 6.5 kpc in the direction (l,b) = (89.°53,+0.°65).

scholarly journals What Do We Really Know About the Winds of Massive Stars?

2007 ◽  
Vol 3 (S250) ◽  
pp. 89-96
Author(s):  
D. John Hillier
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Standard Theory ◽  
Stellar Winds ◽  
X Rays ◽  
X Ray ◽  
Stellar Photosphere ◽  
Weak Winds ◽  
Ionization Balance ◽  
Loss Rates

AbstractThe standard theory of radiation driven winds has provided a useful framework to understand stellar winds arising from massive stars (O stars, Wolf-Rayet stars, and luminous blue variables). However, with new diagnostics, and advances in spectral modeling, deficiencies in our understanding of stellar winds have been thrust to the forefront of our research efforts. Spectroscopic observations and analyses have shown the importance of inhomogeneities in stellar winds, and revealed that there are fundamental discrepancies between predicted and theoretical mass-loss rates. For late O stars, spectroscopic analyses derive mass-loss rates significantly lower than predicted. For all O stars, observed X-ray fluxes are difficult to reproduce using standard shock theory, while observed X-ray profiles indicate lower mass-loss rates, the potential importance of porosity effects, and an origin surprisingly close to the stellar photosphere. In O stars with weak winds, X-rays play a crucial role in determining the ionization balance, and must be taken into account.

scholarly journals Chandra X-ray Observations of Dwarf Starburst Galaxies

2004 ◽  
Vol 217 ◽  
pp. 304-309
Author(s):  
Jürgen Ott ◽  
Fabian Walter ◽  
Elias Brinks ◽  
Ulrich Klein
Keyword(s):  
Interstellar Medium ◽  
Gravitational Potential ◽  
Thermal Plasma ◽  
Theoretical Models ◽  
Starburst Galaxies ◽  
Host Galaxy ◽  
X Ray ◽  
Hot Gas ◽  
Neutral Gas

We obtained X-ray observations for a sample of eight nearby dwarf starburst galaxies from the Chandra X-ray Observatory. Five galaxies of our sample show extended (size: 1-10 kpc), diffuse X-ray emission which can be attributed to a hot thermal plasma. This phase of the interstellar medium purportedly drives the expansion of supergiant shells. A comparison of the derived gas parameters with theoretical models reveals that the hot gas in principle is capable to escape from the gravitational potential of the host galaxy. However, the outflows appear to be contained in those cases where an extended envelope or massive tidal features of neutral gas exist.

scholarly journals Galactic neutral hydrogen and the magnetic ISM foreground

2017 ◽  
Vol 12 (S333) ◽  
pp. 146-150
Author(s):  
S.E. Clark
Keyword(s):  
Interstellar Medium ◽  
Dynamic Range ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Depth Resolution ◽  
High Dynamic Range ◽  
Neutral Gas ◽  
High Dynamic ◽  
New Generation ◽  
The Relationship

AbstractThe interstellar medium is suffused with magnetic fields, which inform the shape of structures in the diffuse gas. Recent high-dynamic range observations of Galactic neutral hydrogen, combined with novel data analysis techniques, have revealed a deep link between the morphology of neutral gas and the ambient magnetic field. At the same time, an observational revolution is underway in low-frequency radio polarimetry, driven in part by the need to characterize foregrounds to the cosmological 21-cm signal. A new generation of experiments, capable of high angular and Faraday depth resolution, are revealing complex filamentary structures in diffuse polarization. The relationship between filamentary structures observed in radio-polarimetric data and those observed in atomic hydrogen is not yet well understood. Multiwavelength observations will enable new insights into the magnetic interstellar medium across phases.

scholarly journals X-ray Emission from Massive Stars at the Core of Very Young Clusters

2016 ◽  
Vol 12 (S329) ◽  
pp. 362-365
Author(s):  
Norbert S. Schulz
Keyword(s):  
Massive Stars ◽  
Stellar Winds ◽  
X Rays ◽  
Stellar Clusters ◽  
Orion Nebula ◽  
X Ray ◽  
The Core ◽  
Hot Plasma ◽  
Young Clusters ◽  
Massive Cluster

AbstractMost cores of very young stellar clusters contain one or more massive stars at various evolutionary stages. Observations of the Orion Nebula Cluster, Trumpler 37, NGC 2362, RCW38, NGC 3603 and many others provide the most comprehensive database to study stellar wind properties of these massive cluster stars in X-rays. In this presentation we review some of these observations and results and discuss them in the context of stellar winds and possible evolutionary implications. We argue that in very young clusters such as RCW38 and M17, shock heated remnants of a natal shell could serve as an alternate explanation to the colliding wind paradigm for the hot plasma components in the X-ray spectra.

scholarly journals Magnetic fields, winds and X-rays of massive stars in the Orion Nebula Cluster

2008 ◽  
Vol 4 (S259) ◽  
pp. 449-452 ◽  
Author(s):  
Véronique Petit ◽  
G. A. Wade ◽  
L. Drissen ◽  
T. Montmerle ◽  
E. Alecian
Keyword(s):  
Magnetic Fields ◽  
Massive Stars ◽  
Magnetic Confinement ◽  
Stellar Winds ◽  
X Rays ◽  
Orion Nebula ◽  
X Ray ◽  
Ob Stars ◽  
Complex Processes ◽  
The Relationship

AbstractIn massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind, resulting in X-ray emission that is harder, more variable and more efficient than that produced by instability-generated shocks in non-magnetic winds. Although magnetic confinement of stellar winds has been shown to strongly modify the mass-loss and X-ray characteristics of massive OB stars, we lack a detailed understanding of the complex processes responsible. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars. In conjunction with a Chandra survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.

scholarly journals Expanding bubbles in Orion A: [C II] observations of M 42, M 43, and NGC 1977

2020 ◽  
Vol 639 ◽  
pp. A2 ◽  
Author(s):  
C. H. M. Pabst ◽  
J. R. Goicoechea ◽  
D. Teyssier ◽  
O. Berné ◽  
R. D. Higgins ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Massive Stars ◽  
Mechanical Energy ◽  
Cosmological Parameters ◽  
Analytical Models ◽  
High Spectral Resolution ◽  
Expansion Velocity ◽  
Stellar Winds ◽  
Orion Nebula ◽  
Expansion Time

Context. The Orion Molecular Cloud is the nearest massive-star forming region. Massive stars have profound effects on their environment due to their strong radiation fields and stellar winds. Stellar feedback is one of the most crucial cosmological parameters that determine the properties and evolution of the interstellar medium in galaxies. Aims. We aim to understand the role that feedback by stellar winds and radiation play in the evolution of the interstellar medium. Velocity-resolved observations of the [C II] 158 μm fine-structure line allow us to study the kinematics of UV-illuminated gas. Here, we present a square-degree-sized map of [C II] emission from the Orion Nebula complex at a spatial resolution of 16′′ and high spectral resolution of 0.2 km s−1, covering the entire Orion Nebula (M 42) plus M 43 and the nebulae NGC 1973, 1975, and 1977 to the north. We compare the stellar characteristics of these three regions with the kinematics of the expanding bubbles surrounding them. Methods. We use [C II] 158 μm line observations over an area of 1.2 deg2 in the Orion Nebula complex obtained by the upGREAT instrument onboard SOFIA. Results. The bubble blown by the O7V star θ1 Ori C in the Orion Nebula expands rapidly, at 13 km s−1. Simple analytical models reproduce the characteristics of the hot interior gas and the neutral shell of this wind-blown bubble and give us an estimate of the expansion time of 0.2 Myr. M 43 with the B0.5V star NU Ori also exhibits an expanding bubble structure, with an expansion velocity of 6 km s−1. Comparison with analytical models for the pressure-driven expansion of H II regions gives an age estimate of 0.02 Myr. The bubble surrounding NGC 1973, 1975, and 1977 with the central B1V star 42 Orionis expands at 1.5 km s−1, likely due to the over-pressurized ionized gas as in the case of M 43. We derive an age of 0.4 Myr for this structure. Conclusions. We conclude that the bubble of the Orion Nebula is driven by the mechanical energy input by the strong stellar wind from θ1 Ori C, while the bubbles associated with M 43 and NGC 1977 are caused by the thermal expansion of the gas ionized by their central later-type massive stars.

scholarly journals A Neutral Gas Jet in a Low Velocity Shock Front at the Boundary of the Draco Nebula

1984 ◽  
Vol 81 ◽  
pp. 243-247 ◽  
Author(s):  
P.W.M. Kalberla ◽  
U. Herbstmeier ◽  
U. Mebold
Keyword(s):  
Shock Front ◽  
Radio Telescope ◽  
High Velocity ◽  
Neutral Hydrogen ◽  
Gas Jet ◽  
Low Velocity ◽  
X Ray ◽  
Neutral Gas ◽  
Thermal Bremsstrahlung

Abstract21-cm line observations with the Westerbork Synthesis Radio Telescope of a dust and molecular filament at the boundary of the Draco Nebula (l≈ 91°, b≈ 38°) reveal a jet-like neutral hydrogen feature funneling through an outlet in the low velocity shock front at the interface between the Draco Nebula and the surrounding gas. The jet-like feature is apparently connected with a high velocity filament at VLSR = -180 km s-1. We suggest that the soft x-ray emission observed in the area is thermal bremsstrahlung produced by the deceleration of high velocity gas in galactic gas.

scholarly journals Star Formation and Molecular Gas in Extremely Metal-poor Galaxies: Insights from the Thermal Balance in the Neutral Gas

2018 ◽  
Vol 14 (S344) ◽  
pp. 259-262 ◽  
Author(s):  
Vianney Lebouteiller
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Large Fraction ◽  
Formation Rate ◽  
Conversion Function ◽  
Molecular Gas ◽  
Apparent Lack ◽  
X Ray ◽  
Heating Mechanism ◽  
Neutral Gas

AbstractThe apparent lack of cold molecular gas in blue compact dwarf (BCD) galaxies is at variance with their intense star-formation episode. The CO molecule, often used a tracer of H2 through a conversion function, is selectively photodissociated in dust-poor environments and, as a result, a potentially large fraction of H2 is expected to reside in the so-called CO-dark gas, where it could be traced instead by infrared cooling lines [CI], [CII], and [OI]. Although the fraction of CO-dark gas to total molecular gas is in theory expected to be relatively large in metal-poor galaxies, many uncertainties remain due to the difficulty in identifying the main heating mechanism associated to the cooling lines observed in such galaxies.Investigations of the Herschel Dwarf Galaxy Survey (DGS; Madden et al.2013) show that the heating mechanism in the neutral gas of BCDs cannot be dominated by the photoelectric effect on dust grains below some threshold metallicity due to the low abundance of dust and polycyclic aromatic hydrocarbons, implying that other heating mechanisms need to be invoked, along with a new interpretation of the corresponding infrared line diagnostics. In the study presented here and in Lebouteiller et al. (2017), we use optical and infrared lines to constrain the physical conditions in the HII region + HI region of the BCD I Zw 18 (18 Mpc; ≍2% solar metallicity) within a consistent photoionization and photodissociation model. We show that the HI region is entirely heated by a single ultraluminous X-ray source with important consequences on the applicability of [CII] to trace the star-formation rate and to trace the CO-dark gas. We derive stringent upper limits on the size of H2 clumps that may be detected in the future with JWST and IRAM/NOEMA. We also show that the nature of the X-ray source can be inferred from the corresponding signatures in the ISM. Finally we speculate that star formation may be quenched in extremely metal-poor dwarf galaxies due to X-ray photoionization.

scholarly journals X-ray diagnostics of massive star winds

2016 ◽  
Vol 12 (S329) ◽  
pp. 151-155
Author(s):  
L. M. Oskinova ◽  
R. Ignace ◽  
D. P. Huenemoerder
Keyword(s):  
High Resolution ◽  
Stellar Wind ◽  
Massive Star ◽  
Massive Stars ◽  
Stellar Winds ◽  
X Rays ◽  
Early Type ◽  
Stellar Rotation ◽  
X Ray ◽  
Early Type Stars

AbstractObservations with powerful X-ray telescopes, such as XMM-Newton and Chandra, significantly advance our understanding of massive stars. Nearly all early-type stars are X-ray sources. Studies of their X-ray emission provide important diagnostics of stellar winds. High-resolution X-ray spectra of O-type stars are well explained when stellar wind clumping is taking into account, providing further support to a modern picture of stellar winds as non-stationary, inhomogeneous outflows. X-ray variability is detected from such winds, on time scales likely associated with stellar rotation. High-resolution X-ray spectroscopy indicates that the winds of late O-type stars are predominantly in a hot phase. Consequently, X-rays provide the best observational window to study these winds. X-ray spectroscopy of evolved, Wolf-Rayet type, stars allows to probe their powerful metal enhanced winds, while the mechanisms responsible for the X-ray emission of these stars are not yet understood.

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