42 research outputs found
Study of vibrational spectra of polycyclic aromatic hydrocarbons with phenyl side group
Computational study of polycyclic aromatic hydrocarbons (PAHs) with phenyl
side group substituted at different positions is reported. The infrared
spectral variations due to the position of phenyl substitution, ionization
state and the size of the molecules are discussed and possible contribution of
phenyl-PAHs to the mid-infrared emission features from astrophysical objects is
analyzed. Structurally phenyl group substitution at 2nd position gives more
stable species compared to substitution at other positions. Phenyl-PAHs exhibit
new aromatic bands near 695 and 741 cm (14.4 and 13.5 m), due to
contribution from quintet C-H wag, that compare well with minor features at
14.2 and 13.5 m observed in several astrophysical objects. Just as in
plain PAHs, the C-C stretch vibrational modes (1600 cm) have
negligible intensity in neutrals, but the cations of all phenyl-PAHs exhibit
significantly strong phenyl group C-C stretch peak close to class B type 6.2
m astrophysical band. In 2-phenylpyrene, it is the neutral molecule that
exhibits this strong feature in the 6.2 m range along with other features
that match with sub-features at 6.66 and 6.9 m, observed in astronomical
spectra of some late type objects. The substitution of phenyl side group at
solo position shifts the C-C stretch mode of parent PAH close to the region of
6.2 m astrophysical band. The results indicate possibility of phenyl-PAHs
in space and the bottom-up formation of medium sized compact PAHs with phenyl
side group in carbon rich cool circumstellar shells. Phenyl-PAHs need to be
considered in modelling mid-infrared emission spectra of various astrophysical
objects.Comment: 45 papges including 15 Figures and 3 Table
Photometric and Kinematic study of the open cluster NGC 1027
We present photometric and kinematic analysis of an intermediate age open
cluster NGC 1027 using and Gaia Early Data Release 3 (EDR3) data.
Structural and fundamental parameters such as cluster center, cluster extent,
reddening, age and distance are estimated in this study. Cluster center is
found about 2 arcmin away from the center reported earlier. Radius has been
estimated to be about 8.00 arcmin(2.65pc). Using proper motion Gaia EDR3 data,
membership probabilities has been derived for the stars in the region of
cluster radius. We find mean proper motion of the cluster to be (-0.84,
2.04) mas yr in (RA, DEC). We find 217 most probable (P 70\%)
cluster members with mean parallax 0.892 0.088 mas. Out of these, 160
members have counterparts in our optical observations. Few stars having
P 70\% are found out of the cluster radius showing imprints of dynamical
evolution. The color-color and color-magnitude diagrams for the cluster members
found within 8.00 arcmin have been constructed using photometry and
Gaia EDR3 data. This yields a reddening E(-) 0.36 mag, age
130 Myr and distance 1.14 kpc. The mass function slope in the cluster
region is -1.46 0.15, which is similar to other Galactic
open clusters. The dynamical study shows lack of faint stars in its inner
region leading to mass segregation effect. A comparison of dynamical age with
cluster age indicates that NGC 1027 is a dynamically relaxed cluster suggesting
that mass segregation may be imprint of its dynamical relaxation
Modeling the interstellar aromatic infrared bands with co-added spectra of PAHs
The observed variations in profiles of the interstellar aromatic infrared
bands correlate with the object type and are indicative of PAH populations
existing i n different sources. Spectroscopic studies on PAHs can provide tools
for the int erpretation of variations accompanying the AIBs. As the observed
spectra results from a mix of possible species in the region attempt is made to
model this comp osite spectra by co-adding emissions from PAHs in different
size groups. Theoretical IR data of PAHs having 10 to 96 carbon atoms is used
to obtain emis sion spectra. The models are taken in size groups making up of
small, medium and large PAHs. The models show good profile match with
observations for the 7.7 complex having sub-features at 7.6 and 7.8
. The 7.6 sub-feature dominates in the spectra of medium sized
PAH cations matching observations from UV rich interstellar environments. The
7.8 component is more intense in the spectra of large PAH cations
(model III) correlating with observations from benign astrophysical regions. A
possible interpretation for the observations of out-of-plane bend modes
and the weak outliers on the blue side of the intense 11.2 band is
proposed. The models provide pointers to possible PAH populations in different
regions.Comment: accepted for publication in A&
The scattering and extinction properties of nanodiamonds
The study of scattering and extinction properties of possible nanodiamond
grains in the ISM are reported. Calculations using Discrete Dipole
Approximation (DDA) for varying ellipsoidal shapes and sizes from 2.5 to are considered. Nanodiamonds show negligible extinction from IR to near-UV
and very sharp far-UV rise. Comparison with observations rule out possibility
of independent nanodiamond dust but point towards possibility of nanodiamonds
as a component in the ISM. Radiation induced transformations may lead to
carbonaceous grains with different core and mantles. So calculations are also
performed for a core-mantle target model with nanodiamond core in graphite
mantles. The graphite extinction features get modified with the peak at 2175
\AA{} being lowered, broadened, blue shifted and accompanied by enhanced
extinction in the far-UV. Such variations in the 2175 \AA{} band and
simultaneous far-UV rise are observed along some sources. A three component
dust model incorporating silicate, graphite and graphite with nanodiamond core
is also considered. The model extinction compares very well with the average
galactic extinction in the complete range from 0.2 to . The best
fit requires small size and small number of nanodiamonds.Comment: Accepted for publication in MNRAS; 8 Figure
Optical intra-day variability of the blazar S5 0716+714
We present an extensive recent multi-band optical photometric observations of
the blazar S5 0716+714 carried out over 53 nights with two telescopes in India,
two in Bulgaria, one in Serbia, and one in Egypt during 2019 November -- 2022
December. We collected 1401, 689, 14726, and 165 photometric image frames in B,
V, R, and I bands, respectively. We montiored the blazar quasi-simultaneously
during 3 nights in B, V, R, and I bands; 4 nights in B, V, and R; 2 nights in
V, R, and I; 5 nights in B and R; and 2 nights in V and R bands. We also took
37 nights of data only in R band. Single band data are used to study intraday
flux variability and two or more bands quasi-simultaneous observations allow us
to search for colour variation in the source. We employ the power-enhanced
F-test and the nested ANOVA test to search for genuine flux and color
variations in the light curves of the blazar on intraday timescales. Out of 12,
11, 53, and 5 nights observations, intraday variations with amplitudes between
~3% and ~20% are detected in 9, 8, 31 and 3 nights in B, V, R, and I bands,
respectively, corresponding to duty cycles of 75%, 73%, 58% and 60%. These duty
cycles are lower than those typically measured at earlier times. On these
timescales color variations with both bluer-when-brighter and
redder-when-brighter are seen, though nights with no measurable colour
variation are also present. We briefly discuss possible explanations for this
observed intraday variability.Comment: 19 pages, 5 figures, 4 tables, Accepted for Publication in MNRA
Proceedings of Abstracts, School of Physics, Engineering and Computer Science Research Conference 2022
© 2022 The Author(s). This is an open-access work distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. For further details please see https://creativecommons.org/licenses/by/4.0/. Plenary by Prof. Timothy Foat, ‘Indoor dispersion at Dstl and its recent application to COVID-19 transmission’ is © Crown copyright (2022), Dstl. This material is licensed under the terms of the Open Government Licence except where otherwise stated. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: [email protected] present proceedings record the abstracts submitted and accepted for presentation at SPECS 2022, the second edition of the School of Physics, Engineering and Computer Science Research Conference that took place online, the 12th April 2022