scholarly journals Imaging and spectroscopy of the LMC He II nebula N 44C and its ionizing star

1999 ◽  
Vol 193 ◽  
pp. 480-481
Author(s):  
Vanessa C. Galarza ◽  
Donald R. Garnett ◽  
You-Hua Chu
Keyword(s):  
Large Magellanic Cloud ◽  
Convincing Evidence ◽  
H Ii Regions ◽  
Uv Spectrum ◽  
Ionized Gas ◽  
X Ray ◽  
H Ii Region ◽  
Recombination Emission ◽  
Imaging And Spectroscopy ◽  
Echelle Spectroscopy

We present results from new HST imaging and spectroscopy of the peculiar Large Magellanic Cloud H II region N 44C and its ionizing star. While this nebula exhibits strong He II recombination emission, the source of the He+ ionizing photons has not been found. The UV spectrum of the ionizing star suggests an approximate spectral class of 07–08; the UV Si IV, He II, and N IV features do not show P-Cygni profiles, indicating that the ionizing star is not a supergiant. No companion star has yet been detected. Ground-based and HST optical spectroscopy of the ionized gas shows that the nebular abundances of C, N, O and He are not anomalous relative to other LMC H II regions, suggesting that no previous WR/SN companion has disappeared. Echelle spectroscopy has also ruled out the presence of high velocity shocked gas. Deep ROSAT imaging shows no X-ray point source in this location. The “fossil X-ray binary” hypothesis of Pakull & Motch (1989) remains the best explanation for the ionization of this nebula; however, convincing evidence for this hypothesis remains elusive.

scholarly journals 3D optical spectroscopic study of NGC 3344 with SITELLE: I. Identification and confirmation of supernova remnants

2019 ◽  
Vol 488 (1) ◽  
pp. 803-829 ◽  
Author(s):  
I Moumen ◽  
C Robert ◽  
D Devost ◽  
R P Martin ◽  
L Rousseau-Nepton ◽  
...  
Keyword(s):  
Supernova Remnants ◽  
Flux Ratio ◽  
Large Magellanic Cloud ◽  
Emission Lines ◽  
Ionization Mechanism ◽  
H Ii Regions ◽  
Nearby Galaxy ◽  
Galactocentric Distance ◽  
Ionized Gas ◽  
Diffuse Ionized Gas

ABSTRACT We present the first optical identification and confirmation of a sample of supernova remnants (SNRs) in the nearby galaxy NGC 3344. Using high spectral and spatial resolution data, obtained with the CFHT imaging Fourier transform spectrograph SITELLE, we identified about 2200 emission line regions, many of which are H ii regions, diffuse ionized gas regions, and also SNRs. Considering the stellar population and diffuse ionized gas background, which are quite important in NGC 3344, we have selected 129 SNR candidates based on four criteria for regions where the emission lines flux ratio [S ii]/H α ≥ 0.4. Emission lines of [O ii] λ3727, H β, [O iii] λλ4959,5007, H α, [N ii] λλ6548,6583, and [S ii] λλ6716,6731 have been measured to study the ionized gas properties of the SNR candidates. We adopted a self-consistent spectroscopic analysis, based on Sabbadin plots and Baldwin, Phillips & Terlevich diagrams, to confirm the shock-heated nature of the ionization mechanism in the candidates sample. With this analysis, we end up with 42 Confirmed SNRs, 45 Probable SNRs, and 42 Less likely SNRs. Using shock models, the confirmed SNRs seem to have a metallicity ranging between Large Magellanic Cloud and 2×solar. We looked for correlations between the size of the confirmed SNRs and their emission lines ratios, their galaxy environment, and their galactocentric distance: We see a trend for a metallicity gradient among the SNR population, along with some evolutionary effects.

scholarly journals Magnetic fields, stellar feedback, and the geometry of H II regions

2008 ◽  
Vol 4 (S259) ◽  
pp. 25-34
Author(s):  
Gary J. Ferland
Keyword(s):  
Magnetic Field ◽  
Magnetic Pressure ◽  
H Ii Regions ◽  
Line Profiles ◽  
Ionized Gas ◽  
Stellar Feedback ◽  
H Ii Region ◽  
Field Lines ◽  
The Magnetic Field ◽  
Simple Picture

AbstractMagnetic pressure has long been known to dominate over gas pressure in atomic and molecular regions of the interstellar medium. Here I review several recent observational studies of the relationships between the H+, H0 and H2 regions in M42 (the Orion complex) and M17. A simple picture results. When stars form they push back surrounding material, mainly through the outward momentum of starlight acting on grains, and field lines are dragged with the gas due to flux freezing. The magnetic field is compressed and the magnetic pressure increases until it is able to resist further expansion and the system comes into approximate magnetostatic equilibrium. Magnetic field lines can be preferentially aligned perpendicular to the long axis of quiescent cloud before stars form. After star formation and pushback occurs ionized gas will be constrained to flow along field lines and escape from the system along directions perpendicular to the long axis. The magnetic field may play other roles in the physics of the H II region and associated PDR. Cosmic rays may be enhanced along with the field and provide additional heating of atomic and molecular material. Wave motions may be associated with the field and contribute a component of turbulence to observed line profiles.

scholarly journals When H ii regions are complicated: considering perturbations from winds, radiation pressure, and other effects

2019 ◽  
Vol 492 (1) ◽  
pp. 915-933 ◽  
Author(s):  
Sam Geen ◽  
Eric Pellegrini ◽  
Rebekka Bieri ◽  
Ralf Klessen
Keyword(s):  
Radiation Pressure ◽  
Large Range ◽  
Massive Stars ◽  
Relative Effect ◽  
H Ii Regions ◽  
Gas Temperature ◽  
Algebraic Models ◽  
Ionized Gas ◽  
Principal Mode ◽  
H Ii Region

ABSTRACT We explore to what extent simple algebraic models can be used to describe H ii regions when winds, radiation pressure, gravity, and photon breakout are included. We (a) develop algebraic models to describe the expansion of photoionized H ii regions under the influence of gravity and accretion in power-law density fields with ρ ∝ r−w, (b) determine when terms describing winds, radiation pressure, gravity, and photon breakout become significant enough to affect the dynamics of the H ii region where w = 2, and (c) solve these expressions for a set of physically motivated conditions. We find that photoionization feedback from massive stars is the principal mode of feedback on molecular cloud scales, driving accelerating outflows from molecular clouds in cases where the peaked density structure around young massive stars is considered at radii between ∼0.1 and 10–100 pc. Under a large range of conditions the effect of winds and radiation on the dynamics of H ii regions is around 10 per cent of the contribution from photoionization. The effect of winds and radiation pressure is most important at high densities, either close to the star or in very dense clouds such as those in the Central Molecular Zone of the Milky Way. Out to ∼0.1 pc they are the principal drivers of the H ii region. Lower metallicities make the relative effect of photoionization even stronger as the ionized gas temperature is higher.

scholarly journals Understanding the Spatial Distributions of the Ionic/Atomic/Molecular/Dust Components in PNe

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 10
Author(s):  
Toshiya Ueta ◽  
Masaaki Otsuka ◽  
Keyword(s):  
Central Star ◽  
H Ii Regions ◽  
Data Sets ◽  
Ionized Gas ◽  
X Ray ◽  
Neutral Gas ◽  
Photoionization Model ◽  
The Universe ◽  
Circumstellar Environment ◽  
Do So

Planetary nebulae (PNe) are often recognized as the hallmark of compact H ii regions in the Universe. However, there exist dusty neutral regions extending beyond the central ionized region. We demonstrate that such dusty neutral regions (also known as photo-dissociation regions, or PDRs) around the central ionized region are significant parts of PNe in terms of energetics and mass. We do so by using our latest dusty photoionization model of NGC 6781 (of 13 parameters) based on one of the most comprehensive panchromatic data sets ever assembled for a PN encompassing from X-ray to radio (of 136 constraining data, including 19 flux densities, 78 line fluxes, and 37 band fluxes). We find that NGC 6781, evolved out of a 2.25–3.0 M ⊙ star located 460 pc away from us, possesses a massive concentration of neutral gas (molecular hydrogen) just beyond the central ionized region and that the amount of ionized gas in NGC 6781 is only 22% of the observationally accounted amount of matter in the circumstellar environment, which itself does not even account for the amount of mass presumably ejected by the central star during the last thermal pulse event according to the latest evolutionary models. This means that the observed nebula in this PN is only the tip of the iceberg.

scholarly journals The 2016 January eruption of recurrent Nova LMC 1968

2019 ◽  
Vol 491 (1) ◽  
pp. 655-679 ◽  
Author(s):  
N P M Kuin ◽  
K L Page ◽  
P Mróz ◽  
M J Darnley ◽  
S N Shore ◽  
...  
Keyword(s):  
Light Curve ◽  
Large Magellanic Cloud ◽  
Recurrence Time ◽  
Uv Spectrum ◽  
Orbital Inclination ◽  
X Ray ◽  
Orbital Phase ◽  
Colour Changes ◽  
Recurrent Nova ◽  
Ir Photometry

ABSTRACT We present a comprehensive review of all observations of the eclipsing recurrent Nova LMC 1968 in the Large Magellanic Cloud which was previously observed in eruption in 1968, 1990, 2002, 2010, and most recently in 2016. We derive a probable recurrence time of 6.2 ± 1.2 yr and provide the ephemerides of the eclipse. In the ultraviolet–optical–IR photometry the light curve shows high variability right from the first observation around 2 d after eruption. Therefore no colour changes can be substantiated. Outburst spectra from 2016 and 1990 are very similar and are dominated by H and He lines longward of 2000 Å. Interstellar reddening is found to be E(B − V) = 0.07 ± 0.01. The super soft X-ray luminosity is lower than the Eddington luminosity and the X-ray spectra suggest the mass of the white dwarf (WD) is larger than 1.3 M⊙. Eclipses in the light curve suggest that the system is at high orbital inclination. On day 4 after the eruption a recombination wave was observed in Fe ii ultraviolet absorption lines. Narrow-line components are seen after day 6 and explained as being due to reionization of ejecta from a previous eruption. The UV spectrum varies with orbital phase, in particular a component of the He ii 1640 Å emission line, which leads us to propose that early-on the inner WD Roche lobe might be filled with a bound opaque medium prior to the re-formation of an accretion disc. Both this medium and the ejecta can cause the delay in the appearance of the soft X-ray source.

scholarly journals The Ying and Yang of the M 83 Nucleus

2009 ◽  
Vol 5 (S267) ◽  
pp. 121-121
Author(s):  
Damián Mast ◽  
Rubén J. Díaz ◽  
Horacio A. Dottori ◽  
María P. Agüero ◽  
Irapuán Rodrigues ◽  
...  
Keyword(s):  
Velocity Field ◽  
Spatial Resolution ◽  
Spiral Galaxy ◽  
Equivalent Width ◽  
Spatial Scales ◽  
Population Synthesis ◽  
Ionized Gas ◽  
X Ray ◽  
Hα Emission ◽  
Imaging And Spectroscopy

The spiral galaxy M 83, an SB(rs)b at only 4.5 Mpc, is a privileged case for study of the detailed physics on spatial scales of a tenth of a parsec. With 3-D spectroscopic observations using CIRPASS on Gemini-S, we studied the ionized gas properties in J-band with spatial resolution of 0.″5 (Figure 1). The Paβ velocity field shows two dynamical centers, neither of them coincident with the bulge center, identified with the optical nucleus (ON) and the hidden nucleus (HN), with masses, within a radius of 10 pc, of MON = (1.8±0.4)× 107M⊙ and MHN = (1.0±0.4)× 107M⊙. Using the Paβ equivalent width together with population synthesis models, we are able to estimate the ages of both mass concentrations, TON = 8 Myr and THN =6–7 Myr. Adding complexity to this puzzling scenario, we used GMOS+Gemini imaging and spectroscopy to study the radio source J133658.3–295105 (Dottori et al. 2008) and find that Hα emission at the position of this source is redshifted by ~130 km s−1 with respect to an M 83 H II region, leading us to face the possibility of that we are witnessing the ejection of an object by gravitational recoil from the M 83 nucleus. A fit to the X-ray spectrum obtained Chandra supports the association between this source and the disk of M 83 by the presence of the Fe Kα line at 6.7 keV.

Ionization fronts in interstellar gas and the expansion of HII regions

1961 ◽  
Vol 253 (1028) ◽  
pp. 277-300 ◽  
Keyword(s):  
Equations Of Motion ◽  
Initial Density ◽  
Neutral Hydrogen ◽  
Similarity Solutions ◽  
Ionization Front ◽  
H Ii Regions ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Ionization Fronts ◽  
H Ii Region

The gas dynamical effects of an expanding nearly fully ionized hydrogen region (H II region), which is associated with the formation of O and B stars, are investigated. The radiation from the hot star is absorbed by the surrounding interstellar gas (mainly neutral hydrogen) and leads to its ionization. Previous analyses have disregarded the internal motions set up in expanding H II regions. Similarity solutions of the equations of motion are presented for spherical and cylindrical problems, thus enabling the effects of groups of stars as well as individual stars to be discussed. For similarity to be applicable the initial density variations of the undisturbed neutral gas have to be like 1/ r ® in the spherical case and like 1/ r in the cylindrical case. This does not, however, limit their use in describing the general picture of events for any other given density distribution. Recombination of the ions and electrons and subsequent re-ionization by radiation within the H II region is allowed for; cooling processes such as that due to the excitation of O<super>+</super> ions are also taken into account. It is shown that the temperature of the ionized gas in the H II region is approximately uniform even though the region as a whole is expanding. Rates of expansion are calculated and it is also determined whether a shock propagates ahead of the ionized gas. In particular for rates of expansion less than about 20 km/s a shock wave occurs ahead, but for speeds greater than about 20 km/s, which would occur in the initial motion, the rate of expansion of the ionized gas is too great and an ‘isothermal’ shock occurs within the H II region. The boundary between the ionized and neutral gases can be regarded as a discontinuity and is termed an ionization front. The present paper is concerned with the propagation of such fronts and accompanying shocks; a companion paper by W. I. Axford investigates the structures of ‘isothermal shock’ and ionization fronts. The lack of uniqueness, which occurs in the present paper, is removed when the results are combined with Axford’s work.

scholarly journals IUE Studies of Luminous X-Ray Binaries

1983 ◽  
Vol 6 ◽  
pp. 648-648
Author(s):  
J.B. Hutchings
Keyword(s):  
Magellanic Clouds ◽  
Thick Shell ◽  
High Luminosity ◽  
Uv Spectrum ◽  
X Ray ◽  
Unique Object ◽  
The Future ◽  
Orbit Inclination ◽  
Supercritical Accretion ◽  
X Ray Binaries

IUE has been used to study 11 high luminosity X-ray binaries, of which 3 are in the Magellanic Clouds. In the supergiant systems, X-ray ionisation bubbles have been found in most cases, leading to a greater understanding of the winds and accretion processes. Further studies of precessing objects such as LMC X-4 with IUE and ST are clearly of considerable interest, relating to X-ray heating and blanketing. Detailed studies of the Cyg X-l ionisation bubble may resolve the long standing puzzle of its orbit inclination and masses. UV continua have furnished valuable information on extinction, temperatures and luminosities, and the presence of non-stellar (i.e. disk) luminosity. Here too, more detailed studies are clearly indicated for the future. A unique object of interest is the LMC transient 0538-66 whose UV spectrum has quasarlike lines and luminosity which varies oppositely to the visible. This may be a case of supercritical accretion generating an optically thick shell (“disk”) about the pulsar.

scholarly journals On the Nature of R 136, the Central Object of 30 Dor. A Comparison by the Galactic Cluster NGC 3603

1984 ◽  
Vol 108 ◽  
pp. 257-258
Author(s):  
Michael Rosa ◽  
Jorge Melnick ◽  
Preben Grosbol
Keyword(s):  
Core Region ◽  
H Ii Regions ◽  
Central Object ◽  
The Core ◽  
Dominant Component ◽  
Galactic Cluster ◽  
H Ii Region

The massive H II region NGC 3603 is the closest galactic counterpart to the giant LMC nebula 30 Dor. Walborn (1973) first compared the ionizing OB/WR clusters of the two H II regions and suggested that R 136, the unresolved luminous WR + 0 type central object of 30 Dor, might be a multiple system like the core region of NGC 3603. Suggestions that the dominant component of R 136, i.e. R 136A, might be either a single or a very few supermassive and superluminous stars (Schmidt-Kaler and Feitzinger 1982, Savage et al. 1983) have recently been disputed by Moffat and Seggewiss (1983) and Melnick (1983), who have presented spectroscopic and photometric evidence to support the hypothesis of an unresolved cluster of stars. We have extended Walborn's original comparison of the apparent morphology of the two clusters by digital treatment of the images to simulate how the galactic cluster would look like if it were located in the LMC

scholarly journals Three generations of stars: a possible case of triggered star formation

2020 ◽  
Vol 496 (1) ◽  
pp. 870-874
Author(s):  
M B Areal ◽  
A Buccino ◽  
S Paron ◽  
C Fariña ◽  
M E Ortega
Keyword(s):  
Star Formation ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Three Generations ◽  
The North ◽  
Western Border ◽  
H Ii Region ◽  
New Generation ◽  
North Western

ABSTRACT Evidence for triggered star formation linking three generations of stars is difficult to assemble, as it requires convincingly associating evolved massive stars with H ii regions that, in turn, would need to present signs of active star formation. We present observational evidence for triggered star formation relating three generations of stars in the neighbourhood of the star LS II +26 8. We carried out new spectroscopic observations of LS II +26 8, revealing that it is a B0 III-type star. We note that LS II +26 8 is located exactly at the geometric centre of a semi-shell-like H ii region complex. The most conspicuous component of this complex is the H ii region Sh2-90, which is probably triggering a new generation of stars. The distances to LS II +26 8 and to Sh2-90 are in agreement (between 2.6 and 3 kpc). Analysis of the interstellar medium on a larger spatial scale shows that the H ii region complex lies on the north-western border of an extended H2 shell. The radius of this molecular shell is about 13 pc, which is in agreement with what an O9 V star (the probable initial spectral type of LS II +26 8 as inferred from evolutive tracks) can generate through its winds in the molecular environment. In conclusion, the spatial and temporal correspondences derived in our analysis enable us to propose a probable triggered star formation scenario initiated by the evolved massive star LS II +26 8 during its main-sequence stage, followed by stars exciting the H ii region complex formed in the molecular shell, and culminating in the birth of young stellar objects around Sh2-90.

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