90,824 research outputs found
A new scheme of radiation transfer in H II regions including transient heating of grains
A new scheme of radiation transfer for understanding infrared spectra of H II
regions, has been developed. This scheme considers non-equilibrium processes
(e. g. transient heating of the very small grains, VSG; and the polycyclic
aromatic hydrocarbon, PAH) also, in addition to the equilibrium thermal
emission from normal dust grains (BG). The spherically symmetric interstellar
dust cloud is segmented into a large number of "onion skin" shells in order to
implement the non-equilibrium processes. The scheme attempts to fit the
observed SED originating from the dust component, by exploring the following
parameters : (i) geometrical details of the dust cloud, (ii) PAH size and
abundance, (iii) composition of normal grains (BG), (iv) radial distribution of
all dust (BG, VSG & PAH).
The scheme has been applied to a set of five compact H II regions (IRAS
18116- 1646, 18162-2048, 19442+2427, 22308+5812 & 18434-0242) whose spectra are
available with adequate spectral resolution. The best fit models and inferences
about the parameters for these sources are presented.Comment: 16 pages total including 3 tables and 2 figure
Reissner Nordstr\"{o}m Background Metric in Dynamical Co-ordinates: Exceptional Behaviour of Hadamard States
We cast the Reissner Nordstrom solution in a particular co-ordinate system
which shows dynamical evolution from initial data. The initial data for the
case is regular. This procedure enables us to treat the metric as a
collapse to a singularity. It also implies that one may assume Wald axioms to
be valid globally in the Cauchy development, especially when Hadamard states
are chosen. We can thus compare the semiclassical behaviour with spherical dust
case, looking upon the metric as well as state specific information as
evolution from initial data. We first recover the divergence on the Cauchy
horizon obtained earlier. We point out that the semiclassical domain extends
right upto the Cauchy horizon. This is different from the spherical dust case
where the quantum gravity domain sets in before. We also find that the
backreaction is not negligible near the central singularity, unlike the dust
case. Apart from these differences, the Reissner Nordstrom solution has a
similarity with dust in that it is stable over a considerable period of time.
The features appearing dust collapse mentioned above were suggested to be
generally applicable within spherical symmetry. Reissner Nordstrom background
(along with the quantum state) generated from initial data, is shown not to
reproduce them
Purposes almost infinitely varying: archives as sources for labour biography
Sir Hilary Jenkinson, sometime Deputy Keeper of the United Kingdom Public Record
Office, wrote in his Manual of Archive Administration about the two common
features of archives ‘of extraordinary value and importance’: Impartiality and
Authenticity. He referred to the purposes for creating archives and the purposes to
which they are put:
Drawn up for purposes almost infinitely varying – the administrative or
executive control of every species of human undertaking – [archives] are
potentially useful … for the information they can give on a range of subjects
totally different and equally wide … the only safe prediction concerning the
Research ends which Archives may be made to serve is that … these will not
be the purposes which were contemplated by the people by whom the
Archives were drawn up and preserved.1
That is, archives created for one purpose will invariably end up being used for another
purpose entirely. This is challenging for archivists tasked to decide what it is we keep
and what we let go: the fact that we need to predict future research use when not even
those creating the records know to what uses they will be put
Distance, magnetic field and kinematics of a filamentary cloud LDN 1157
LDN 1157, is one of the several clouds situated in the cloud complex, LDN
1147/1158, represents a coma-shaped morphology with a well-collimated bipolar
outflow emanating from a Class 0 protostar, LDN 1157-mm. The main goals of this
work are (a) to map the inter-cloud magnetic field (ICMF) geometry of the
region surrounding LDN 1157 to investigate its relationship with the cloud
morphology, with the outflow direction and with the core magnetic field (CMF)
geometry inferred from the mm- and sub-mm polarization results from the
literature, and (b) to investigate the kinematic structure of the cloud. We
carried out R-band polarization observations of the stars projected on the
cloud to map the pc-scale magnetic field geometry and made spectroscopic
observations of the entire cloud in 12CO, C18O and N2H+ (J=1-0) lines to
investigate its kinematic structure. We obtained a distance of 3403 pc to
the LDN 1147/1158, complex based on the Gaia DR2 parallaxes and proper motion
values of the three YSOs associated with the complex. A single filament of
pc in length and pc in width is found to run all along the
coma-shaped cloud. Based on the relationships between the ICMF, CMF, filament
orientations, outflow direction, and the presence of an hour-glass morphology
of the magnetic field, it is likely that the magnetic field had played an
important role in the star formation process in LDN 1157. Combining the proper
motions of the YSOs and the radial velocity of LDN 1147/1158 and another
complex LDN 1172/1174 which is situated \dgr~east of it, we found that
both the complexes are moving collectively toward the Galactic plane. The
filamentary morphology of the east-west segment of LDN 1157 may have formed as
a result of mass lost by ablation due to the interaction of the moving cloud
with the ambient interstellar medium.Comment: 20 pages, Accepted in Astronomy & Astrophysics, Abstract has been
shortened due to word limit in arxi
Investigation of Non-Stable Processes in Close Binary Ry Scuti
We present results of reanalysis of old electrophotometric data of early type
close binary system RY Scuti obtained at the Abastumani Astrophysical
Observatory, Georgia, during 1972-1990 years and at the Maidanak Observatory,
Uzbekistan, during 1979-1991 years. It is revealed non-stable processes in RY
Sct from period to period, from month to month and from year to year. This
variation consists from the hundredths up to the tenths of a magnitude.
Furthermore, periodical changes in the system's light are displayed near the
first maximum on timescales of a few years. That is of great interest with
regard to some similar variations seen in luminous blue variable (LBV) stars.
This also could be closely related to the question of why RY Sct ejected its
nebula.Comment: 11 pages, 6 figures, 2 table
Detection of steam in the circumstellar disk around a massive Young Stellar Object
We report on the observation of hot water vapor (steam) in the inner AU of a
young massive star located in the star-forming region IRAS 08576-4334. The
water lines are detected in a medium resolution (R=10,000) K-band spectrum
taken by the infrared spectrometer ISAAC mounted on the VLT-ANTU. The water
vapor is at a mean temperature of 1565+/-510 K, cooler than the hot CO found in
the same object, which is at 1660K and the column density is N(H2O)=(2.5 +/-
0.4)x1E18 cm-2. The profile of both H2O and CO lines is best reproduced by the
emission from a Keplerian disk. To interpret the data, we also investigate the
formation of molecules and especially CO and water vapor in the inner hot and
dense part of disks around young high mass stars using a pseudo time-dependent
gas-phase chemical model. Molecules are rapidly photodissociated but this
destruction is compensated by an efficient formation due to fast
neutral-neutral reactions. The ability of CO molecules to self-shield
significantly enhances its abundance. Water molecules are sufficiently abundant
to be detectable. The observed H2O/CO ratio is reproduced by gas at 1600K and
an enhanced UV field over gas density ratio I_UV/nH=1E(-4)- 1E(-6). The
simulations support the presence of CO and H2O molecules in the inner disks
around young massive stars despite the strong UV radiation and show that the OH
radical plays an essential role in hot gas chemistry.Comment: 15 pages, 11 figures, Accepted to A&
Interstellar extinction towards open clusters and galactic structure
We study the distribution of interstellar matter near the galactic plane on
the basis of open star clusters and reviewed the correlation of extinction with
different physical parameters of the clusters to understand the galactic
structure. It is seen from the extinction towards open clusters that about 90%
of the absorbing material lie within -5<b<5 deg of the galactic plane. The mean
thickness of the absorbing material, which is determined in terms of half-width
value \beta, is estimated to be about 125+/-21 pc. We show that the
interstellar absorption follows a sinusoidal variation with galactic longitude
and maximum and minimum absorptions occur at l ~ 48+/-4 deg and l ~ 228+/-4 deg
respectively. It is found that the galactic plane defined by the reddening
material is inclined by an angle of 0.6+/-0.4 deg to the formal galactic plane
and inclination is maximum at l ~ 54+/-6 deg. The reddening analysis has been
used to constrain the Solar offset which is found to be about 22.8+/-3.3 pc
above the reddening plane. We obtained a scale height of 53+/-5 pc for the
distribution of open clusters while it is 186+/-25 pc for the distribution of
reddening material from the reddening plane.Comment: 9 pages, 12 figures, accepted for the publication in MNRA
Lady Caroline Lamb Before Byron: The Godfrey Vassal Webster Affair
This article provides an overview of the love affairs of Lady Caroline Lamb. Before she met Lord Byron, she had a long messy affair with Godfrey Vassal Webster. Their affair was known through letters which was held in the British library, the public records office in Chichester, and the like. Caroline cannot or will not adapt to the complicated social milieu of regency London
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