-
Notifications
You must be signed in to change notification settings - Fork 0
/
research.html
228 lines (212 loc) · 16.4 KB
/
research.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
<!doctype html>
<html lang="en">
<head>
<title>Dr.Santosh Joshi</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<link href="https://fonts.googleapis.com/css?family=Open+Sans:300,400,700,800|Playfair+Display:,300, 400, 700" rel="stylesheet">
<link rel="stylesheet" href="css/bootstrap.css">
<link rel="stylesheet" href="css/animate.css">
<link rel="stylesheet" href="css/owl.carousel.min.css">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/mediaelement@4.2.7/build/mediaelementplayer.min.css">
<link rel="shortcut icon" href="img/favicon.ico"/>
<link rel="stylesheet" href="fonts/ionicons/css/ionicons.min.css">
<link rel="stylesheet" href="fonts/fontawesome/css/font-awesome.min.css">
<!-- Theme Style -->
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<style>
p {
text-align: justify;
color: #2F4F4F;
}
h6{
text-align: justify;
color: black;
}
</style>
<div class="site-wrap">
<a href="#" class="offcanvas-toggle js-offcanvas-toggle" style="background-color: white;box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
border-radius: 25px;
background: white;
padding: 7px;">Menu</a>
<div class="offcanvas_menu" id="offcanvas_menu">
<ul class="mb-5" >
<li><a href="index.html" style="font-size: 13px;">Bio</a></li>
<li><a href="experience.html" style="font-size: 13px;">Professional Experience</a></li>
<li class="active"><a href="research.html" style="font-size: 13px;">Research</a></li>
<li ><a href="publication.html" style="font-size: 13px;">Publication</a></li>
<li><a href="students.html" style="font-size: 13px;">Students</a></li>
<li><a href="teaching.html" style="font-size: 13px;">Teaching</a></li>
<li><a href="internationalProjects.html" style="font-size: 13px;">International Projects</a></li>
<li style="padding-left: 10px;"><a href="binaProject.html" style="font-size: 12px;">1. Bina Project</a></li>
<li style="padding-left: 10px;"><a href="capeSurvey.html" style="font-size: 12px;">2. Cape Survey Project</a></li>
<li><a href="collaborations.html" style="font-size: 13px;">Collaborations</a></li>
<li><a href="collaborators.html" style="font-size: 13px;">Collaborators</a></li>
<li><a href="visits.html" style="font-size: 13px;">Visits</a></li>
<li><a href="confrences.html" style="font-size: 13px;">Confrences & Workshops</a></li>
<li><a href="works.html" style="font-size: 13px;">Important Works</a></li>
<li><a href="outreach.html" style="font-size: 13px;">OutReach</a></li>
<li><a href="gallery.html" style="font-size: 13px;">Gallery</a></li>
<li><a href="contact.html" style="font-size: 13px;">Contact</a></li>
</ul>
<ul class="social" >
<li><a href="#" class="fa fa-twitter"></a></li>
<li><a href="https://www.facebook.com/santosh.joshi.58152" class="fa fa-facebook"></a></li>
<li><a href="mailto:santosh@aries.res.in" class="ion-android-mail"></a></li>
</ul>
<br></div>
<a style="padding-left: 100px;" href="index.html" class="home-button"><span class="fa fa-home"></span></a>
<div id="menu2" style="padding: 50px 100px;" >
<br>
<b>Research Activities</b><br>
<p>The main domain of my primary research lie in the areas of optical astronomy involving time series
analysis of variable stellar sources such as:</p>
<ul>
<li><h6>Asteroseismology of Pulsating Stars</h6></li>
<li><h6>Time-resolved Photometric Analysis of Chemical Peculiar Stars</h6></li>
<li><h6>Chemical Abundance Analysis of the Variable Stars</h6></li>
<li><h6>Census of the Variable Stars in Open and Intermediate Age Star Clusters</h6></li>
<li><h6>Intra-night Variability of Blazars</h6></li>
</ul>
<p> Though, I am involved in many research elds of astronomy and astrophysics but in the following
sub-sections, I have mention only some of front-line research areas where I am participating actively
:</p>
<br>
<h3> Fast Photometric Variability in Chemically Peculiar Stars</h3>
<p >
We have been conducting an Indo-South African bilateral project The Nainital-Cape Survey" since
1999 between ARIES Nainital and South African Astronomical Observatory (SAAO), South Africa.
In last fteen years, more than 300 sample stars were examined for the pulsations, making it one of
the longest ground-based surveys for pulsation in CP stars in terms of time span and sample size.
The main aim of this survey is to nd new pulsating Ap and Am stars in Northern and Southern
hemispheres and set-up test bed to perform the asteroseismic study. Under this project, we discov-
ered rapid oscillation (also known as rapidly oscillating Ap star) in an Ap star HD12098 and Scuti
type pulsation in seven Am stars namely HD13038, HD13079, HD25515 HD98851, HD102480,
HD113878 and HD118660. The more detail information on the Indo-South African project can be
access through the URL http://www.aries.res.in/cns/
This survey programme has been nancially supported by DST Govt. of India and NRF, South
Africa.</p>
<h3>High-Resolution Spectroscopy and Spectro-Polarimetry of Pulsating CP stars</h3>
<p>
For the detailed spectroscopic study of CP stars, in year 2008 we initiated an observing programme
in the collaboration of the Russian astronomers. To achieve our goals, the high-resolution spec-
troscopic observations of the sample Ap and Am stars discovered under the The Nainital-Cape
Survey" were carried out from 6.0-m Russian telescope of Special Astrophysical Observatory (SAO),
Russia. Such observations are very useful to study the pulsation phase of individual spectral lines
and their locations in the chemically strati ed atmosphere. The radial velocity (RV) measurements
of individual spectral line in peculiar stars enable us to measure the pulsational phase and amplitude
of the stellar oscillations as a function of the atmospheric height. The time resolved radial velocity
observations were also used to con rm the variability detected through the photometric observations.
The combined photometric and spectroscopic analysis of these stars have been used in estimating
the basic physical parameters such as e ective temperature, surface gravity, magnetic eld strength
and presence of chemical elements in their atmosphere.
This project was initiated in the collaboration of astronomers from Russia and was supported by
DST Govt. of India and Russian Academy of Science (RAS), Russia under the ILTP and RFBR
programs.</p>
<h3>Census of the Variable Stars in Open and Intermediate Age Star Clusters</h3>
<p>
Open star clusters are excellent tracers to understand astrophysical problems concerning to star
formation and stellar evolution. In order to investigate the occurrence of pulsation in A- and F-
type stars in different galactic environments, we took an initiative in year 2008 to search for the
photometric variability in a well de ned set of young and intermediate age open star clusters. We
selected sample of 25 open star clusters of different age, metallicity and galacto-centric position
where probabilities of nding A-type pulsators are relatively high. For an example, using ground
based time-series photometric observations of an open star cluster NGC6866, we discovered 28 new
variables stars. Our photometric observations were also used for the estimation of the basic physical
parameters and kinematic study of the clusters under study. The photometric analysis of the other
clusters are in progress and we are expecting more interesting results from the data we have collected
2
using the observing facilities of ARIES.
This project is being carried out in the collaboration of astronomers from India, Russia and South
Africa.</p>
<h3>Study of Pulsational Variability and Rotational Activities using Kepler Data</h3>
<p>
We have been also studying the open star clusters and eld stars using combined space and ground
based time-series photometric data obtained on various facilities at di erent epochs.</p>
<h2>Open Star Clusters</h2><br>
<p>After the launch of the Kepler mission on 07 March 2009, enormous of the data have been downloaded
at the NASA MAST science center. Though the primary objective of Kepler mission was to nd the
earth like planets in habitable zones in Cygnus and Lyra regions but this mission has also observed
thousands of stars to probe the interior of the stars and study the stellar evolution using asteroseismic
technique. Coincidentally one of the cluster NGC6866 observed extensively using 1.04-m telescope
of ARIES also falls on the Kepler eld. Using the time-series data extracted from the Kepler archive
data base, we discovered 31 Scuti, 8
Doradus, 23 red giants with solar-like oscillations, 4 eclipsing
binaries and 106 stars showing rotational modulation indicative of star-spots. The combined space
and ground based data were also used to disentangle the cluster members to the non-members for
estimation of age, reddening in the direction of cluster, distance and other parameters used to study
the morphology of the cluster.</p><br>
<h2>Orbital solutions for new spectroscopic systems in Kepler database</h2><br>
<p>This project intend to perform high-resolution spectroscopy for a selection of AF-type candidate
hybrid variable stars detected by the Kepler mission. The proposal's objectives are: 1) to complete
the phase coverage of the orbits by monitoring the long-term behavior in radial velocity (RV) of
the new systems and 2) to determine accurate stellar atmospheric properties and v sini for each of
the components. Here, we propose to extend the time base of the spectroscopic data for 13 new
and suspected long-period SB1/2/3 systems recently observed with the Hermes spectrograph. The
immediate goal of the HCT observations is to analyse and model the composite spectra in order to
derive reliable orbital periods and solutions, as well as to improve upon the component properties of
these systems.
This project is being carried out in the collaboration of astronomers from India and Belgium under
the Belgo-India Network on Astronomy and Astrophysics.</p><br>
<h2>Field stars</h2><br>
<p>We have studied the time-series photometric analysis of about 15000 eld stars observed by the
Kepler space mission. We measured rotation periods of 2270 active stars as a function of spectral
type and studied the distribution of their amplitudes. We examined the period-color relationship
for rotational variables and found that this relationship holds for early-F to early A-type stars. In-
terestingly, we found that this relation is not consistent with the period-age-mass (PtM) relation
that was previously anticipated. Through the visual inspection of the light curves and periodograms,
we con rmed the solar-like oscillations in 16 red giant stars and identi ed 75 additional solar-like
oscillations. The basic parameters such as masses, radii and luminosities of these solar-like oscilla-
tors are estimated using the asteroseismic scaling relation. We have characterized several non-radial
pulsating variables as Sct,
Dor and hybrid stars. The relationship between two newly constructed
observable, energy" and efficiency" for these stars have also been reported. Our results support
that the present observational instability strip should be extended towards the red end of instability
strip to accommodate the Sct and
Dor variables.
3
This project is being carried out in the collaboration of astronomers from India, Belgium and
South Africa.</p><br>
<h2> Low-resolution Spectroscopy of the Kepler Stars</h2><br>
<p>For the detailed study of a star one need to estimate the basic parameters such as e ective tem-
perature, gravity because these parameters acts as an input for the stellar models. We used the
low-resolution spectroscopic observations of the Kepler stars from 6.0-m telescope at SAO, Russia,
2.0-m telescope of HCT India and the Large Sky Area Multi-Object Fibre Spectroscopic Telescope
(LAMOST) at China. All the spectra were analysed using ULySS (University of Lyon spectroscopic
software) as well as standardized routines in IRAF package. On comparison of two data sets analysed
using two di erent techniques, we found that the low-resolution spectroscopic data can be also used
to estimated the basic parameters such as e ective temperature, gravity etc.
This work is being carried out under the collaboration of astronomers from India, South Africa
and Belgium.</p><br>
<h2>Intra-night Variability of Blazars</h2><br>
<p>Rapid light variations are seen in many Quasars and almost in all the Blazars. The amount of vari-
ability in di erent classes of active galactic nuclei has been studied extensively but many questions
remain unanswered. To characterize the intra-night optical variability(INOV) of TeV Blazars and
Quasars, we monitored a well de ned sets of objects in optical bands. These observations play an
important role in understanding the link between the dominant varieties of powerful active galactic
nucleus and comparison of the characteristics of the two major sub-classes of TeV Blazars. The
physical processes responsible for producing INOV of Blazars continue to be debated. For simulta-
neous measurements on intra-night variability on di erent time-scale we used various Indian optical
telescopes for photometry and the KANATA telescope of Japan for imaging polarimetry. Besides the
quiescent slowly varying emission, the Blazars display
ares on time scales as short as minutes, we
have assumed a two component model responsible for producing a long term and short term
aring
trends.
This work is being carried out in the collaborations among the astronomers from India, Japan and
Poland.
</p> </div>
</div>
<!-- loader -->
<div id="loader" class="show fullscreen"><svg class="circular" width="48px" height="48px"><circle class="path-bg" cx="24" cy="24" r="22" fill="none" stroke-width="4" stroke="#eeeeee"/><circle class="path" cx="24" cy="24" r="22" fill="none" stroke-width="4" stroke-miterlimit="10" stroke="#f4b214"/></svg></div>
<script src="js/jquery-3.2.1.min.js"></script>
<script src="js/popper.min.js"></script>
<script src="js/bootstrap.min.js"></script>
<script src="js/owl.carousel.min.js"></script>
<script src="js/jquery.waypoints.min.js"></script>
<script src="js/jquery.countdown.min.js"></script>
<script src="js/main.js"></script>
</body>
</html>