scholarly journals Planned Observations of Hot Gas in the LISM

1997 ◽  
Vol 166 ◽  
pp. 95-98
Author(s):  
R. McLean ◽  
J.C. Green ◽  
K.S. Gunderson
Keyword(s):  
High Resolution ◽  
Column Density ◽  
Signal To Noise Ratio ◽  
Gas Absorption ◽  
Line Profiles ◽  
Local Interstellar Medium ◽  
Local Bubble ◽  
Hot Gas ◽  
Production Models ◽  
Oxygen Profiles

AbstractWe plan to observe hot gas in the local interstellar medium (LISM) at high resolution using a rocket-borne spectrograph that can simultaneously observe OVI, NV and CIV at resolutions of 1 – 2kms−1. Data from a single flight will have sufficient signal to noise ratio to detect a broad 50kms−1 component down to a column density of N ≥ 0.5 × 1013cm−2. High-velocity components as fast as 300kms−1 can be detected. New high resolution observations of hot gas absorption line profiles will probe the kinematics of the local bubble, and comparison between the carbon, nitrogen and oxygen profiles will allow discrimination between the various production models.

scholarly journals HI and Hot Gas in the Outskirts of the M81 Group

2004 ◽  
Vol 217 ◽  
pp. 452-457 ◽  
Author(s):  
M. Bureau ◽  
F. Walter ◽  
J. van Gorkom ◽  
C. Carignan
Keyword(s):  
High Resolution ◽  
Column Density ◽  
Dwarf Galaxies ◽  
Star Forming ◽  
Hot Gas ◽  
External Group ◽  
Ram Pressure ◽  
Tidal Tails ◽  
Velocity Cloud ◽  
High Velocity Cloud

Results are presented from a wide area, high resolution HI synthesis survey of the outer regions of the nearby M81 group, where internal (galactic) and external (group-related) evolution processes can be studied simultaneously in great detail. The survey encompasses the star forming dwarf galaxies M81dwA, UGC4483, and HoII, where evidence of ram pressure stripping was recently discovered. The data do not reveal any intergalactic HI, but the outer parts of HoII are reminiscent of tidal tails. We argue however that those structures are equally consistent with the latest ram pressure models including cooling. The case for a hot intergalactic medium in this poor, spiral-only group is thus still open. The survey also puts tight constraints on possible counterparts to the local high velocity cloud population in an external group, reaching a 3σ column density of 1019 atom cm−2 and a 6σ limiting mass of 1.5 × 105M⊙.

scholarly journals Stellar contributions to the line profiles of high-resolution transmission spectra of exoplanets

2018 ◽  
Vol 617 ◽  
pp. A134 ◽  
Author(s):  
F. Borsa ◽  
A. Zannoni
Keyword(s):  
High Resolution ◽  
Line Profile ◽  
Transmission Spectrum ◽  
Signal To Noise Ratio ◽  
Transmission Spectra ◽  
Line Profiles ◽  
Stellar Rotation ◽  
Stellar Spectra ◽  
Exoplanetary Atmospheres ◽  
Sophisticated Analysis

Context. In-depth studies of exoplanetary atmospheres are starting to become reality. In order to unveil their properties in detail, we need spectra with a higher signal-to-noise ratio (S/N) and also more sophisticated analysis methods. Aims. With high-resolution spectrographs, we can not only detect the sodium feature in the atmosphere of exoplanets, but also characterize it by studying its line profile. After finding a clearly w-shaped sodium line profile in the transmission spectrum of HD 189733b, we investigated the possible sources of contamination given by the star and tried to correct for these spurious deformations. Methods. By analyzing the single transmission spectra of HD 189733b in the wavelength space, we show that the main sodium signal that causes the absorption in the transmission spectrum is centered on the stellar rest frame. We concentrate on two main stellar effects that contaminate the exoplanetary transmission spectrum: center-to-limb variations (CLVs) and stellar rotation. We show the effects on the line profile: while we correct for the CLV using simulated theoretical stellar spectra, we provide a new method, based directly on observational data, to correct for the Rossiter–McLaughlin contribution to the line profile of the retrieved transmission spectrum. Results. We apply the corrections to the spectra of HD 189733b. Our analysis shows line profiles of the Na D lines in the transmission spectrum that are narrower than reported previously. The correction of the sodium D2 line, which is deeper than the D1 line, is probably still incomplete since the planetary radius is larger at this wavelength. A careful detrending from spurious stellar effects followed by an inspection in the velocity space is mandatory when studying the line profile of atmospheric features in the high-resolution transmission spectrum of exoplanets. Since the line profile is used to retrieve atmospheric properties, the resulting atmospheric parameters could be incorrectly estimated when the stellar contamination is not corrected for. Data with higher S/N coupled with improved atmospheric models will allow us to adapt the magnitude of the corrections of stellar effects in an iterative way.

scholarly journals Infrared Emission from Interstellar Dust in the Local Interstellar Medium

1997 ◽  
Vol 166 ◽  
pp. 353-362
Author(s):  
W.T. Reach ◽  
F. Boulanger
Keyword(s):  
Interstellar Medium ◽  
Radiation Field ◽  
Spatial Correlation ◽  
Column Density ◽  
Interstellar Dust ◽  
Infrared Emission ◽  
Dust Content ◽  
Local Interstellar Medium ◽  
Local Bubble ◽  
Total Column

AbstractIn this contribution, we discuss some topics in the study of dust in the local interstellar medium. The spectrum of local clouds has recently been measured using ISO and COBE, confirming in general the models of excitation and cooling of dust illuminated by the the interstellar radiation field. We discuss in some detail the spatial correlation of interstellar dust and gas and the idea that infrared emission traces the total column density of the interstellar medium, with the particular application to the formation of H2. We also show that dust is present in the nearby Loop I shell, with properties similar to average, suggesting that the walls of the Local Bubble would also have relatively ‘normal’ dust content.

High-resolution Na I Observations of the Local Interstellar Medium

1991 ◽  
Vol 9 (1) ◽  
pp. 122-123
Author(s):  
Barry Y. Welsh ◽  
Peter W. Vedder ◽  
John V. Vallerga
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
Column Density ◽  
Velocity Structure ◽  
Extreme Ultraviolet ◽  
Sodium Absorption ◽  
Local Interstellar Medium ◽  
Neutral Gas ◽  
Hydrogen Column Density ◽  
Early Type Stars

AbstractWe present high-resolution absorption measurements (R ~ 150 000) of the interstellar Na I D-lines at 5890 Å observed towards 46 early-type stars. The distance to these stars ranges from 20–200 pc, allowing a probe of the local interstellar medium (LISM). The velocity structure, velocity dispersions and column densities of the various cloud components have been derived using an absorption line-fitting analysis. Sodium column densities have been determined for 23 of the 46 target stars. No sodium absorption was detected towards any of the stars with distances < 43 pc. Such null results imply a corresponding hydrogen column density limit, N(H), of ~ 2.5 × 1018cm−2 in many directions in the LISM. For three exceptionally vacant lines of sight (to β CMa, 36 Lyn and η Hya) this limit of low hydrogen column density can be placed out to a much further distance of > 150 pc.We have plotted the distribution of sodium column density in the LISM for a total of 118 stars in the form of three galactic maps. These maps qualitatively show that the present picture of the LISM, in which the first 50 pc is essentially free of dense clumps of neutral gas, is correct. Our map of sodium columns for stars with distances > 100 pc shows that the region within the galactic quadrant defined by 200° < l < 270° shows a conspicuous absence of any significant concentration of neutral gas. This region will be a prime direction of study for forthcoming soft X-ray and extreme ultraviolet satellite experiments.

scholarly journals [C II] 158 μm self-absorption and optical depth effects

2020 ◽  
Vol 636 ◽  
pp. A16 ◽  
Author(s):  
C. Guevara ◽  
J. Stutzki ◽  
V. Ossenkopf-Okada ◽  
R. Simon ◽  
J. P. Pérez-Beaupuits ◽  
...  
Keyword(s):  
Optical Depth ◽  
Column Density ◽  
Signal To Noise Ratio ◽  
Far Infrared ◽  
Emission Lines ◽  
High Spectral Resolution ◽  
Line Of Sight ◽  
High Signal ◽  
Line Profiles ◽  
Star Forming

Context. The [C II] 158 μm far-infrared fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). It is used as a tracer of star formation efficiency in external galaxies and to study feedback effects in parental clouds. High spectral resolution observations have shown complex structures in the line profiles of the [C II] emission. Aims. Our aim is to determine whether the complex profiles observed in [12C II] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [12C II] and isotopic [13C II] line profiles. Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the sources of M43, Horsehead PDR, Monoceros R2, and M17 SW allow for the detection of optically thin [13C II] emission lines, along with the [12C II] emission lines, with a high signal-to-noise ratio. We first derived the [12C II] optical depth and the [C II] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [C II] gas: column density and excitation temperature. Results. We find moderate to high [12C II] optical depths in all four sources and self-absorption of [12C II] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent Av of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [C II] gas, with an equivalent Av ranging up to about 13 mag. Conclusions. The column density of the warm background material requires multiple photon-dominated region surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [C II] gas detected in absorption cannot be explained with any known scenario and we can only speculate on its origins.

scholarly journals Modeling the Local Bubble Using Multiple Supernova Remnants

1997 ◽  
Vol 166 ◽  
pp. 133-136
Author(s):  
R.K. Smith ◽  
D.P. Cox
Keyword(s):  
Interstellar Medium ◽  
Supernova Remnants ◽  
Local Interstellar Medium ◽  
Local Bubble ◽  
One Dimensional ◽  
X Ray ◽  
Hot Gas ◽  
Sky Survey ◽  
Non Equilibrium

AbstractWe have modeled the Local Bubble (LB) using a one-dimensional hydrocode (ODIN) that can simulate multiple supernova remnants, with non-equilibrium ion evolution and dust. Our model assumes that the local interstellar medium was a cool (104 K) gas approximately 5-10 Myr ago; it was then disturbed by 2 or 3 supernovae exploding within 20-30 pc of each other over a period of 2-4 million years. The LB is the leftover hot gas from these explosions. The model predicts the x-ray emission from such a bubble, as well as ionic abundances for hot gas ions such as O VI. These are compared to the soft x-ray data from the Wisconsin all-sky survey and the ROSAT PSPC.

Non-LTE model atmosphere analyses of faint PN central stars observed with Keck HIRES

1997 ◽  
Vol 180 ◽  
pp. 120-121
Author(s):  
James K. McCarthy ◽  
Roberto H. Méndez ◽  
R.-P. Kudritzki
Keyword(s):  
High Resolution ◽  
Signal To Noise Ratio ◽  
Model Atmosphere ◽  
Helium Abundance ◽  
Line Profiles ◽  
Signal To Noise ◽  
Echelle Spectrograph ◽  
First Results ◽  
Central Stars ◽  
Temperature Surface

We are engaged in using the HIRES echelle spectrograph (Vogt et al. 1994) on the 10 m Keck I Telescope to significantly increase the number of central stars of planetary nebulae (CSPN) studied spectroscopically at high resolution and signal-to-noise ratio. With Keck we are able to extend our previous work (Méndez et al. 1988, 1992; McCarthy 1988) to much fainter magnitudes. In short, comparisons of the observed HI Balmer, HeI, and He II line profiles to the Munich grid of plane-parallel non-LTE model atmosphere line profiles provide distance- and nebula-independent determinations of CSPN effective temperature, surface gravity, and helium abundance. For CSPN showing wind emission, the comparisons are made to new “unified” models (reviewed by Kudritzki et al., this meeting) which include radiation-driven winds. The first results of this on-going program are shown below.

scholarly journals Analysis of High Resolution Stellar Line Profiles

1980 ◽  
Vol 51 ◽  
pp. 75-84
Author(s):  
David F. Gray
Keyword(s):  
High Resolution ◽  
Spectral Line ◽  
Spectral Resolution ◽  
Signal To Noise Ratio ◽  
Physical Phenomenon ◽  
Velocity Fields ◽  
Line Profiles ◽  
Late Type ◽  
Signal To Noise ◽  
Line Shapes

High resolution implies that we obtain some information on spectral line shapes. In late-type stars, we need to measure velocities of a few km/sec to accomplish this. Increasing the spectral resolution and the signal to noise ratio allows us to progress step by step toward deeper physical understanding. The steps we take often lead to good debate and “stimulate” our lives. I am sometimes amused at the urgency we feel to press on to the next step. We rarely seem to pause and enjoy the completion of previous steps. Perhaps this is because we always see shortcomings in completed work. Quite typically one will “discover” the importance of some physical phenomenon (It makes little difference how many others already know about it.), and in his eyes everything done previously becomes wrong because this phenomenon was not included. We used to hear how Milne-Eddington or Schuster-Schwarzschild model atmospheres were inadequate -we had to use instead properly computed depth dependence. We used to hear how LTE models were no good - we had to use more detailed physics. Now we talk about line analyses being inadequate because it has not included velocity fields. The curious thing is that we believe that including our pet phenomenon gives the correct models. We ignore all those other phenomena as yet unseen! (Is this a mechanism for maintaining sanity?) I think it really amounts to a statement of what we are able to measure, compute, or understand.

Progress in high-resolution CRYO-SEM imaging of viral particles

1996 ◽  
Vol 54 ◽  
pp. 818-819
Author(s):  
Ya Chen ◽  
Geoffrey Letchworth ◽  
John White
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
High Resolution ◽  
Structural Information ◽  
Signal To Noise Ratio ◽  
Flexible Structures ◽  
Simian Virus ◽  
Topographic Features ◽  
Viral Particles ◽  
Scanning Electron

Low-temperature high-resolution scanning electron microscopy (cryo-HRSEM) has been successfully utilized to image biological macromolecular complexes at nanometer resolution. Recently, imaging of individual viral particles such as reovirus using cryo-HRSEM or simian virus (SIV) using HRSEM, HV-STEM and AFM have been reported. Although conventional electron microscopy (e.g., negative staining, replica, embedding and section), or cryo-TEM technique are widely used in studying of the architectures of viral particles, scanning electron microscopy presents two major advantages. First, secondary electron signal of SEM represents mostly surface topographic features. The topographic details of a biological assembly can be viewed directly and will not be obscured by signals from the opposite surface or from internal structures. Second, SEM may produce high contrast and signal-to-noise ratio images. As a result of this important feature, it is capable of visualizing not only individual virus particles, but also asymmetric or flexible structures. The 2-3 nm resolution obtained using high resolution cryo-SEM made it possible to provide useful surface structural information of macromolecule complexes within cells and tissues. In this study, cryo-HRSEM is utilized to visualize the distribution of glycoproteins of a herpesvirus.

scholarly journals The stratified disc wind of MCG-03-58-007

2020 ◽  
Vol 500 (1) ◽  
pp. 291-300
Author(s):  
V Braito ◽  
J N Reeves ◽  
P Severgnini ◽  
R Della Ceca ◽  
L Ballo ◽  
...  
Keyword(s):  
Absorption Line ◽  
Velocity Component ◽  
Column Density ◽  
Accretion Disc ◽  
Line Profiles ◽  
Lower Velocity ◽  
Multiple Observations ◽  
Two Phases ◽  
The One ◽  
High Column

ABSTRACT Past Suzaku, XMM–Newton, and NuSTAR observations of the nearby (z = 0.03233) bright Seyfert 2 galaxy MCG-03-58-007 revealed the presence of two deep and blue-shifted iron K-shell absorption line profiles. These could be explained with the presence of two phases of a highly ionized, high column density accretion disc wind outflowing with vout1 ∼ −0.1c and vout2 ∼ −0.2c. Here we present two new observations of MCG-03-58-007: one was carried out in 2016 with Chandra and one in 2018 with Swift. Both caught MCG-03-58-007 in a brighter state ($F_{{\mathrm{2}-10\, keV}} \sim 4 \times 10^{-12}$ erg cm−2 s−1) confirming the presence of the fast disc wind. The multi-epoch observations of MCG-03-58-007 covering the period from 2010 to 2018 were then analysed. These data show that the lower velocity component outflowing with vout1 ∼ −0.072 ± 0.002c is persistent and detected in all the observations, although it is variable in column density in the range NH ∼ 3–8 × 1023 cm−2. In the 2016 Swift observation we detected again the second faster component outflowing with vout2 ∼ −0.2c, with a column density ($N_{\mbox{H}}=7.0^{+5.6}_{-4.1}\times 10^{23}$ cm−2), similar to that seen during the Suzaku observation. However during the Chandra observation 2 yr earlier, this zone was not present (NH &lt; 1.5 × 1023 cm−2), suggesting that this faster zone is intermittent. Overall the multi-epochs observations show that the disc wind in MCG-03-58-007 is not only powerful, but also extremely variable, hence placing MCG-03-58-007 among unique disc winds such as the one seen in the famous QSO PDS456. One of the main results of this investigation is the consideration that these winds could be extremely variable, sometime appearing and sometime disappearing; thus to reach solid and firm conclusions about their energetics multiple observations are mandatory.

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