scholarly journals Spatial Correlations of Selected DIBs to the CH and CH+ Molecules

2013 ◽  
Vol 9 (S297) ◽  
pp. 128-131
Author(s):  
T. Weselak ◽  
J. Krełowski
Keyword(s):  
Equivalent Width ◽  
Column Density ◽  
Radial Velocities ◽  
The Other ◽  
Spatial Correlations ◽  
Ob Stars ◽  
Other Hand

AbstractThe analysis of radial velocities in the spectra of HD 151932 and HD 152233, performed for the optical lines of interstellar CH and CH+ molecules on one hand, and for the diffuse bands 4964 and 6196 Å on the other hand, suggests that the carrier of the former DIB is spatially related to CH, while the carrier of the latter - to CH+. A further analysis, based on the sample of 106 reddened OB stars, partly confirms this suggestion, showing that the CH column density correlates indeed much better with the equivalent width of the 4964 DIB than with that of the 6196 DIB.

scholarly journals Chemical Analysis of B stars within 9–11 kpc from the Galactic Center

2009 ◽  
Vol 5 (S265) ◽  
pp. 362-363
Author(s):  
Maria Isela Zevallos Herencia ◽  
Simone Daflon
Keyword(s):  
Chemical Analysis ◽  
Galactic Center ◽  
Thin Disk ◽  
Open Clusters ◽  
The Other ◽  
Galactocentric Distance ◽  
B Stars ◽  
Ob Stars ◽  
Other Hand ◽  
Chemical Distribution

AbstractRadial gradients of metallicity are supported by observations of different young objects in the Galactic thin disk. The shape of the abundance distributions, however, is not completely constrained. Some works describe the abundance distributions as a function of the Galactocentric distance RG by linear fits with a single slope. On the other hand some analyses of open clusters, cepheids and OB stars suggest a discontinuity in the abundance distributions around RG=10 kpc. In this work we analyse a sample of 13 B stars members of four open clusters located within RG=9-11 kpc in order to better constrain the chemical distribution in this region of the disk.

scholarly journals A Multi-Frequency Study of the Peculiar Interacting System ARP 206

1990 ◽  
Vol 124 ◽  
pp. 69-73
Author(s):  
Louis Noreau ◽  
Philipp P. Kronberg
Keyword(s):  
Radial Velocities ◽  
The Other ◽  
Interacting Galaxies ◽  
Other Hand ◽  
First Case

Arp 206 is a nearby (7.8 Mpc), relatively large (7′.5 x 2′.0), and bright ( = 11.07) interacting system comprising unequal members: NGC 3432 and UGC 5983. A third anonymous galaxy, “Arp 206c”, is visible in the field, (see Figure la) Vorontsov-Velyaminov (1959) included the NGC 3432-UGC 5983 pair in his Atlas and Catalogue of Interacting Galaxies (VV-11). On the other hand Arp (1966) interpreted the system as a galaxy with material ejected from the nucleus (Arp 206).Bertola (1966, 1968, and priv. comm.) obtained long-slit spectra of the largest galaxy of the pair, NGC 3432. This showed strong non-circular motions that could be interpreted as an explosion in its nucleus. This work is in line with a similar study of another system, Arp 205 (Bertola et al. 1983, Noreau and Kronberg 1986, 1987). In this first case it was found that the non-circular radial velocities were caused by the ‘re-entry’ of galactic material torn away by the interacting system.

scholarly journals On the Origin of Metallicity in Lyman-Alpha Forest Systems

2002 ◽  
Vol 187 ◽  
pp. 123-127
Author(s):  
M. Chiba ◽  
B. B. Nath
Keyword(s):  
High Resolution ◽  
Column Density ◽  
Large Fraction ◽  
The Other ◽  
Absorption Lines ◽  
Lyman Alpha ◽  
Other Hand ◽  
Lyman Alpha Forest

Several recent observations indicate that even the low H I column density Lyα absorption lines may not be primordial, as they were previously thought to be. High-resolution observations using the Keck telescope (Cowie et al. 1995; Tytler et al 1995.; Songaila & Cowie 1996) have revealed that a large fraction of Lyα absorption lines with H I column density as low as NHI ~ 1014 cm−2 at redshift z ~ 3 are associated with metal lines (C IV). This fraction, hereafter denoted as fm, is estimated as 0.5-0.75. On the other hand, there is an indication that at low z a large fraction of Lyα absorption lines are directly associated with halos of visible galaxies. This fraction is hereafter denoted as fg. Lanzetta et al. (1995, hereafter LBTW) claimed fg ~ 0.6 at z ≲ 1 (see also Bowen, Pettini & Boyle 1997).

scholarly journals The relation between 5780 and 5797 diffuse interstellar bands, CH/CH+ molecules, and atomic or molecular hydrogen

2019 ◽  
Vol 625 ◽  
pp. A55 ◽  
Author(s):  
T. Weselak
Keyword(s):  
Correlation Coefficient ◽  
Equivalent Width ◽  
Atomic Hydrogen ◽  
Molecular Hydrogen ◽  
Column Density ◽  
Width Ratio ◽  
Ob Stars ◽  
Diffuse Interstellar Bands ◽  
Molecular Fraction

Correlations between column densities of neutral and molecular hydrogen and strengths of major 5780 and 5797 Å diffuse interstellar bands (DIBs) based on spectra of 66 OB stars were analyzed. We confirm that the 5797 Å DIB is more tightly correlated with column density of molecular hydrogen while the 5780 DIB – with that of atomic hydrogen. This leads to a reasonably tight relation between the molecular fraction of H2 and equivalent width ratio of the 5797 and 5780 major diffuse bands with correlation coefficient equal to 0.77 ± 0.05. Column densities of CH and CH+ molecules were used to analyze correlations between abundances of CH/CH+ molecules and strengths of the major 5780 and 5797 DIBs. The 5780 DIB is better correlated with the column density of methydyline cation than the 5797 DIB. A relation with correlation coefficient equal to 0.95 ± 0.02 based on precise column densities, between column densities of CH and H2 molecules, is also presented; in other words, the column densitiy ratio in the case of H2 and CH molecules in the ISM is equal to (2.01 ± 0.09) × 107.

scholarly journals Are there carbon stars in the Bulge?

1999 ◽  
Vol 191 ◽  
pp. 545-550
Author(s):  
Yuen Keong Ng
Keyword(s):  
Star Formation ◽  
Radial Velocity ◽  
Velocity Dispersion ◽  
Dwarf Galaxy ◽  
Radial Velocities ◽  
The Other ◽  
Agb Stars ◽  
Carbon Stars ◽  
Other Hand

The Bulge carbon stars have been a mystery since their discovery by Azzopardi et al. (1991), because they are about too faint to be regarded as genuine AGB stars, if located inside the metal-rich Bulge . Part of the mystery can be solved if these carbon stars are related to the Sagittarius dwarf galaxy . They are in that case not old and metal-rich, but young, ∼0.1 Gyr, with SMC-like metallicity (Ng 1998).The σRV = 113 ± 14 km s−1 (Tyson & Rich 1991) radial velocity dispersion of the stars appears to be consistent with Bulge membership. On the other hand, a similar velocity dispersion could be the result from an induced star formation event when the SDG crosses the galactic midplane. It is suggested that the carbon stars are tracers of such an event and that they therefore are located at distances related to the SDG. However, the majority of the carbon stars are not member of the SDG, nor are they similar to the C-stars which are member of the SDG.The radial velocities can be used to determine a possible membership to the SDG. However, they do not give information about the distance of the stars. In particular, if the stars are located at a distance comparable to the SDG. This implies that only the period-luminosity relation (Groenewegen & Whitelock 1996) can be used to distinguish unambiguously if the carbon stars are located at Bulge-like or SDG-like distances. Thus far only carbon stars with reliable periods have been identified at a SDG related distance (Ng & Schultheis 1997; Whitelock 1998).

scholarly journals A new assessment of the kinematic distance to the Pleiades: based on radial velocities and proper motions only

2012 ◽  
Vol 8 (S289) ◽  
pp. 66-69
Author(s):  
S. Röser ◽  
E. Schilbach
Keyword(s):  
Maximum Velocity ◽  
Radial Velocities ◽  
The Other ◽  
Cluster Method ◽  
Distance Modulus ◽  
Proper Motions ◽  
A Value ◽  
Other Hand ◽  
Error Bars

AbstractWe present a new determination of the distance to the Pleiades using the moving-cluster method, allowing for inclusion of the effects of expansion and rotation of the cluster. While rotation appears neglegible, we find a slight expansion of the cluster with a maximum velocity of 0.15 km s−1 and a distance modulus of (m − M)0 = 5.50 ± 0.13 mag. This is larger but compatible with the new Hipparcos distance modulus of 5.40 ± 0.03 mag. On the other hand, various distance moduli for the Pleiades are found in the literature, many resulting from isochrone fitting. They scatter around a value of 5.63 mag. Our results are also compatible with these measurements, within the error bars.

scholarly journals Understanding the Galaxy

2017 ◽  
Vol 14 (S339) ◽  
pp. 50-55
Author(s):  
L. Eyer
Keyword(s):  
Time Domain ◽  
Major Part ◽  
Milky Way ◽  
Radial Velocities ◽  
The Other ◽  
General Overview ◽  
Other Hand ◽  
The Galaxy ◽  
Disc Bulge ◽  
The One

AbstractThis general overview of our understanding of the Galaxy followed the lines of its main structures (halo, disc, bulge/bar) and emphasized some time-domain astronomy contributions. On the one hand the distance and tangential motions of the stars are essential to that understanding, and are obtained through multi-epoch surveys. On the other hand the chemistry of the stars and their radial velocities are also key elements for mapping the Galactic (sub-)structures, and unravelling their history and evolution. Contemporary surveys are revolutionizing our view of the Milky Way and of galaxies in general. Among those, the Gaia mission excels through its precise astrometry of 1.3 billion stars that populate the Milky Way and beyond, providing the first 3-D view of a major part of the Milky Way.

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

Life Beyond 1MeV

1980 ◽  
Vol 38 ◽  
pp. 30-33
Author(s):  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
Past Experience ◽  
The Other ◽  
Good Case ◽  
Other Hand ◽  
The U.S

Life beyond 1MeV – like life after 40 – is not too different unless one takes advantage of past experience and is receptive to new opportunities. At first glance, the returns on performing electron microscopy at voltages greater than 1MeV diminish rather rapidly as the curves which describe the well-known advantages of HVEM often tend towards saturation. However, in a country with a significant HVEM capability, a good case can be made for investing in instruments with a range of maximum accelerating voltages. In this regard, the 1.5MeV KRATOS HVEM being installed in Berkeley will complement the other 650KeV, 1MeV, and 1.2MeV instruments currently operating in the U.S. One other consideration suggests that 1.5MeV is an optimum voltage machine – Its additional advantages may be purchased for not much more than a 1MeV instrument. On the other hand, the 3MeV HVEM's which seem to be operated at 2MeV maximum, are much more expensive.

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