Question
Asked 22nd Aug, 2018

How to use virtual observatories in doing scientific research in astrophysics?

Hi All!! I have recently completed my PhD in theoretical astrophysics with work on accretion flow around black holes. Now I want to venture into some observational studies. I would like to know how I can make use of the VIRTUAL OBSERVATORIES to start some good quality research work in observations. I would be very glad if you could share some useful links or documents. Thanking you all...

Most recent answer

25th Aug, 2018
P.K. Karmakar
Tezpur University
Thanks for details

All Answers (4)

23rd Aug, 2018
P.K. Karmakar
Tezpur University
How do you distinguish between real observatories and virtual observatories? Could you set up an organic linkage?
24th Aug, 2018
Archana Bora
Gauhati University
A Virtual observatory provides user a virtual platform to get access to astronomical large data base, user friendly softwares for processing and analyzing the data. The Virtual Observatory India project (http://voi.iucaa.in/voi/abouVOI.htm) is one such platform. Link to other virtual observatory sites can be found at http://voi.iucaa.in/voi/linkstosites.htm.
2 Recommendations
25th Aug, 2018
Biplob Sarkar
Tezpur University
Thank you Archana Bora Madam for the very helpful answer.
Dear P.K. Karmakar Sir, the concept of a Virtual Observatory (VO) has been very clearly explained by Archana Madam. Moreover, I want to specify that the VO is an accumulation of protocols that make it less demanding to fabricate applications against archival astronomical data (in addition to other things). It is a misnomer in that it isn't generally an observatory in any capacity. Nowadays, although we can access astronomical data online anywhere, the crucial aspect is to learn about the computational techniques and data analysing techniques.
25th Aug, 2018
P.K. Karmakar
Tezpur University
Thanks for details

Similar questions and discussions

Does the Supernova Chain Reaction Follows [C]^2?
Question
6 answers
  • Marco PereiraMarco Pereira
The goal of this question was for e to provide a proof that the Absolute Peak Luminosity of type 1A Supernovae have a G^(-3) dependence.
The argument is correct but it seems to be too complex.
There is a simpler argument that people can understand better.  Just follow these links.
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Supernovae distances are mapped to the Absolute Peak Luminosity of their light profiles. This means the the only two measured values are luminosity at the peak and and 15 days later (to measure width).
Supernova explodes through a nuclear chain reaction:
1) C+C->Mg
2) Mg+O->Ca
3) Ca+O->Ni
4) Ni->Co->Fe 
Luminosity is equal to the number of Ni atoms decay per second or dNidt.
So the peak Luminosity is the Peak dNidt. 
There are TWO considerations that together support my approximation:
a) The detonation process accelerates 2-3 reactions (in comparison with equilibrium rates prior to detonation).
b) The detonation process adds a delay to photon diffusion. The shock wave originated in the core will travel to the surface. When the shock wave arrives at the surface, reaction 1-3 should (in principle) stop. Ejecta (non burned residues) are then eject and the photons resulting from the Ni decay have to diffuse through the thick ejecta cloud.
If you look into the Light/[C]^2 curve, you will realize that is has a small delay with respect to Light curve.  The constraint of having a finite star size forces the maximum absolute peak luminosity to synchronize itself with the maximum peak Magnesium rate dMgdt, which happens at the maximum radius. So, the Physics of a finite star and a shockwave nuclear chemistry process forces the Peak Absolute Luminosity (dNidt) to match the maximum rate of Magnesium formation (dMgdt). Implicit in this conclusion is the idea that the pressure and temperature jump expedites intermediate fusions.
My contention is:
a) Light has to go through a diffusion process while traveling from the core. The motion of the detonation curve might synchronize light and [C]^2
b) The model in the python script contains a parameter associated with the light diffusional process leading to the peak luminosity.
I would love to hear about the chosen rate values (I used arbitrary values that would provide a time profile in the order of the observed ones). I would appreciate if you had better values or a model for rewriting the equations for the nuclear chain reaction.
I see the detonation process as a Mg shock wave propagating through the star. Light would follow that layer and thus be automatically synchronized with [C]^2
Under these circumstances, volumetric nuclear chemistry depicted in the python script would have to be replaced by shockwave chemistry.  That would certainly be only dependent upon the Mg content on the shockwave and thus make light be directly proportional to [C]^2!!!
In Summary:
HU see the Supernova Light process to be proportional to [C]^2.  This assertion has support on two mechanisms:
  1. Detonation temperature increase will increase the rate of equations 2-3
  2. Detonation process should be modeled as a nuclear chemistry shockwave where Mg is being consumed as fast as it is being created. Light is following this shockwave and will peak by the time the shockwave reaches the surface of the Star.  So, the shockwave mechanism ties together light diffusion and Carbon nuclear chemistry.
Since I wrote this, I followed up on my own suggestion and considered the shockwave nuclear chemistry approach. You can download all my scripts at the github below.
The shockwave model considers that the amount of light on a cell along the shockwave is is the integrated light created through its evolution. It is developed as a unidimensional process since the observation (billions of years away from the supernova) can be construed as having only contributions from all the cells along the radial line connecting us to the Supernova.
So, the model is unidimensional. That said, it contains all the physics of a tri-dimensional simple model. All rates are effective rates since during the Supernova explosion nuclear reactions are abundant (one can have tremendous variations on neutron content).
The physics is the following:
a) White Dwarf reaches epoch-dependent Chandrasekhar mass. Compression triggers Carbon detonation A shockwave starts at the center of the White Dwarf
b) That shockwave induces 2C->Mg step. The energy released increases local temperature and drive second and third equation to the formation of Ni.  Ni decay releases photons.
c) Photons follow the shockwave and diffuse to the surface where we can detect them. The shockwave takes tc to reach the Chandrasekhar radius (surface of the White Dwarf).
d) Luminosity comes from the Ni decay from the element of volume plus the aggregate photons traveling with the shockwave. They diffuse to the surface
e) Two diffusion rates are considered. One for light diffusion within the Star and another for diffusion in the ejecta.
# Diffusion process with two rates 0.3 for radiation created before the shockwave
# reaches surface and 0.03 for radiation diffusion across ejecta
kdiff=0.3*(t<tc)-0.03*(t>tc)
f) I considered tc to be 15 days, that is, it takes 15 days for peak luminosity. Changing this value doesn't change the picture.
g) The peak luminosity is matched to the peak Magnesium formation at t=tc or when the shockwave reaches the Star surface.
This means that Physics makes the Absolute Luminosity Peak to be also the peak of Magnesium formation and that takes place at the Star surface.

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