India's Space based Telescopes and Astronomical spacecraft

[Indx TechStyle]

Feb 27, 2018
AstroSat Picture of the Month (January 2018)
DETECTION OF MILLI-SECOND TIMING PHENOMENA BY LAXPC
X-ray binaries are a special class of binary stars that are very bright in X-rays. The X-rays are produced when matter is accreted from the donor star (usually a relatively normal star) onto the accretor, which is very compact – a Neutron Star or Black Hole.

4U 1728-34 is a Neutron Star low mass X-ray binary (NS-LMXB) which is known to exhibit regular thermo-nuclear bursts (Type-I) of accreted matter onto the Neutron Star surface. The burst oscillations (BO) observed during the initial phase of the Type-1 burst is one of the important diagnostic tool to measure the spin period of the NS-LMXB.

In addition to BO, which originates at the surface of NS, quasi-periodic oscillations (QPO) of X-ray radiation from the accreting gas is also a common phenomenon observed in X-ray binaries. QPOs in milliseconds timescale are very important tool to understand the dynamics of accretion flow at the close vicinity of the compact objects.

The source 4U 1728-34 was observed by LAXPC onboard AstroSat on 8th March 2016 for ~ 3 ksec duration. Dynamical power density spectrum in the 3-20 keV band during the observation, reveals the presence of a high frequency QPO (HFQPO) whose frequency drifted from ~ 815 Hz at the beginning of the observation to about 850 Hz (fig.1). The QPO is also detected, for the first time in the 10-20 keV band by LAXPC (fig.2).

Fig.1: Dynamic power spectra of HFQPO in the energy range 3-20 keV. X-axis shows time evolution of frequency of QPO. Y-axis shows frequency in Hz. Colour coding indicates the power.

Fig.2: Power spectrum of HFQPO in the energy range 10 – 20 keV
During the end part of LAXPC observation of the source, a typical Type-1 burst was detected, and the count rate in the detector reached ∼10000 c/s. The burst profile is typical with a fast rise and slow decay lasting for ~20 seconds (fig.3).

Fig.3: Time profile of the Type-I X-ray burst observed with LAXPC
In the early phase of the burst, a coherent burst oscillation was observed at around 363 Hz. The frequency varies from ~361.5 to ~363.5 Hz which has been reported by Rossi X-ray Timing Explorer (RXTE) during earlier burst observations.

Thus LAXPC demonstrated the capability of detecting millisecond timing phenomenon even from short observations.

Reference:Jai Verdhan Chauhan et.al., The Astrophysical Journal, 841:41 (5pp), 2017 May 20
Ctsy: isro.gov.in

 

[Indx TechStyle]

Feb 28, 2018
AstroSat Picture of the Month (Science Day-February 2018)
The Witch’s Broom in the sky

Image Credits: F. K. Sutaria, K.P. Singh, P. T. Rahna, J. Murthy, A.K. Ray and N.K. Rao

The Witch's Broom or the Western Veil, is a part of a large Supernova Remnant called the Cygnus Loop or the Veil Nebula. Extending over 3 degrees in the sky (compared to the full moon which is 0.5 degrees), and located in the northern constellation of Cygnus, the entire Cygnus Loop is 75 light years in diameter, and around 1470 light years away. Though the nebula is one of the most beautiful and colorful objects in the sky, it is quite faint due to its large angular size and a big telescope in a dark sky is needed to fully appreciate it in all its glory.

Different parts of this object were discovered separately and given different names. The Witch's Broom, or NGC 6960 is a part of this gigantic Supernova Remnant. This remnant is the result of a very massive star exploding sometime between 3000 and 6000 B.C. The shock waves of this explosion, as they blast through the surrounding gas, produce emission in all bands of light, including radio, visible, ultra-violet and X-rays. Since the expanding shells are extremely thin and is almost transparent to background optical light, only the edges are bright enough to see. This is why we see fine filaments or ropes that resemble a broom.

The Near Ultra-Violet and Far Ultra-Violet images of the Witch's Broom captured by AstroSat's UVIT show emission from these delicate glowing filaments, primarily from ionized Silicon, Carbon, Iron and Helium. Astronomers are using this data to study the chemicals in this gas, and how they are heated by the shock of the explosion.

 

[Chinmoy]

Feb 28, 2018
AstroSat Picture of the Month (Science Day-February 2018)
The Witch’s Broom in the sky

Image Credits: F. K. Sutaria, K.P. Singh, P. T. Rahna, J. Murthy, A.K. Ray and N.K. Rao

The Witch's Broom or the Western Veil, is a part of a large Supernova Remnant called the Cygnus Loop or the Veil Nebula. Extending over 3 degrees in the sky (compared to the full moon which is 0.5 degrees), and located in the northern constellation of Cygnus, the entire Cygnus Loop is 75 light years in diameter, and around 1470 light years away. Though the nebula is one of the most beautiful and colorful objects in the sky, it is quite faint due to its large angular size and a big telescope in a dark sky is needed to fully appreciate it in all its glory.

Different parts of this object were discovered separately and given different names. The Witch's Broom, or NGC 6960 is a part of this gigantic Supernova Remnant. This remnant is the result of a very massive star exploding sometime between 3000 and 6000 B.C. The shock waves of this explosion, as they blast through the surrounding gas, produce emission in all bands of light, including radio, visible, ultra-violet and X-rays. Since the expanding shells are extremely thin and is almost transparent to background optical light, only the edges are bright enough to see. This is why we see fine filaments or ropes that resemble a broom.

The Near Ultra-Violet and Far Ultra-Violet images of the Witch's Broom captured by AstroSat's UVIT show emission from these delicate glowing filaments, primarily from ionized Silicon, Carbon, Iron and Helium. Astronomers are using this data to study the chemicals in this gas, and how they are heated by the shock of the explosion.

Just wonder how marvellous the output of ASTROSAT-2 would be...... .

Just watching other day the attempt of creating a 3D map of our universe. It was awesome and breathtaking at its best.

 

[Indx TechStyle]

Sep 28, 2018

Three years of AstroSat​

AstroSat, India’s first space observatory class satellite dedicated to Astronomy, was launched onboard PSLV from Satish Dhawan Space Centre SHAR, Sriharikota on September 28, 2015 into a low earth orbit. After the first six months of calibration and verification phase, the observatory started observing cosmos in multi-wavelength spanning a wide range from near Ultraviolet (UV) to High Energy X- rays.

AstroSat carries a total of five scientific payloads, namely, Ultra-Violet Imaging Telescope (UVIT), Soft X-ray Telescope (SXT), Large Area X-ray Proportional Counter (LAXPC), Cadmium Zinc Telluride Imager (CZTi) and Scanning Sky Monitor (SSM). AstroSat has provided good spatial resolution images in UV over half degree field of view and has a large collecting area at High Energy X-rays (LAXPC). Except for SSM, other four payloads onboard AstroSat are co-aligned and capable of performing simultaneous observations of astronomical sources. The observations were carried out based on the proposals received from users in India and abroad. AstroSat has observed more than 750 sources till September 2018. For the proposal cycle starting from October 2018, around 150 of them are approved and scheduled for observations.

From the beginning, AstroSat is providing good results. Data from AstroSat has resulted in close-to 100 publications in refereed journals, and this number is expected to increase with the data now made open to public on September 26, 2018. (Archival Data of AstroSat released).

AstroSat has provided several new and exciting results like

• Solving the decade old puzzle of a cool red star but bright in UV, by identifying it as a binary

• X-ray polarisation from Crab nebula

• Detection of a coronal explosion on the nearest planet-hosting star (simultaneously observed by NASA’s Chandra X-ray observatory and Hubble Space Telescope)

The Ultraviolet Tails of the “Atoms for Peace” galaxy (NGC 7252). Image Credits: Koshy George et al., 2018.

UVIT image of Witch's Broom, part of Veil Nebula. Image Credits: F. K. Sutaria et al.

 

[Indx TechStyle]

Sep 26, 2018

Archival Data of AstroSat released​

AstroSat, ISRO’s first satellite dedicated to Astronomy was launched on September 28, 2015. Five Scientific payloads were flown onboard AstroSat. The multi-wavelength observations started six months after the launch and providing world-class data from Ultra Violet to High Energy X-rays.

AstroSat data was opened to public by the Chairman, ISRO / Secretary DOS on September 26, 2018. Data from all the payloads, Ultra-Violet Imaging Telescope (UVIT), Soft X-ray Telescope (SXT), Large Area X-ray Proportional Counter (LAXPC), Cadmium Zinc Telluride (CZT) and Scanning Sky Monitor (SSM) are made opene for users around the world. These archival data are available for download from Indian Space Science Data Centre (ISSDC) at AstroBrowse.

The released AstroSat data consists of observations on Supernova Remnants, Active Galactic Nuclei, galactic clusters and several other exciting astronomical objects providing opportunities for studying the cosmos from UV to X-rays for users.

Three colour composite image of NGC 2336 in NUV (Green) and FUV (Blue) with 2MASS-K band (red). Image from Rahna et. al, 2018.

 

[Indx TechStyle]

ISRO, NASA just spotted a black hole spinning so fast that it could be making space itself rotate

• India’s AstroSat and NASA’s Chandra X-Ray Observatory have confirmed the discovery of a black hole spinning close to the maximum possible speed.
• A black hole spinning that fast can make space itself rotate according to Einstein’s theory of relativity.
• This black hole is only one of five to have an accurately measured high spin rate.
• Researchers hypothesise that this could be the key to understanding how galaxies are formed.

Black holes, while fascinating, aren’t a new discovery. But, a black hole spinning at one of the highest speeds ever is a whole other story. Especially when there have only ever been four others like it.

India’s first dedicated astronomy satellite, the AstroSat spotted a black hole in the binary star system called 4U 1630-47 that’s spinning close to the maximum speed possible. NASA’s Chandra X-Ray Observatory confirmed the high spin rate.

This particular ‘monster black hole’ is spinning very close to the limit set by Albert Einstein’s theory of relativity according to Rodrigo Nemmen, the lead author on the research paper. That means anything that’s being pulled into the black hole is being pulled in at the speed of light.

Currently, scientists only have two ways of measuring black holes – either by their mass or by their spin rate. And, a spin rate can be anywhere between 0 and 1. This black hole was spinning at the rate of 0.9.

Einstein’s theory further implies that if a black hole spinning that fast, then it is capable of making space itself rotate.

In fact, if the conditions around black holes are hypothesised to be correct, then the high spin rate couple with the gaseous elements entering the black hole and high temperatures, could be the key to understanding how galaxies are formed.

Including the black hole discovered by the AstroSat, there are only five black holes have accurately measured high spin rates. Even if you’re not taking spin rates into account, this black hole of one of only 20 others that have been spotted in the Milky Way Galaxy.

The Indian Space Research Organisation’s (ISRO) AstroSat along with the National Aeronautics and Space Administration’s (NASA) Chandra X-Ray Observatory have confirmed the speed of the spinning black hole.

The study was conducted by researchers from multiple institutions led by the Tata Institute of Fundamental Research (TIFR) and has been accepted for publication in The Astrophysical Journal.

 

[Chinmoy]

ISRO's AstroSat Discovers Ultraviolet Wings on the Butterfly Nebula

https://thewire.in/the-sciences/isros-astrosat-discovers-ultraviolet-wings-on-the-butterfly-nebula

Pune

: Indian astrophysicists have discovered large ultraviolet lobes and jets, hurled out from a dying star, using data from AstroSat, the space observatory launched by the Indian Space Research Organisation (ISRO) in 2015. The discovery has been featured as the AstroSat Picture of the Month (APOM) for October.

Kameswara Rao of the Indian Institute of Astrophysics and his collaborators used the Ultra-Violet Imaging Telescope (UVIT) on board AstroSat to study a planetary nebula called NGC 6302, popularly called the Butterfly Nebula. A planetary nebula is formed when a star like our Sun – or a few times heavier – is in its dying days. The term, a misnomer now, was coined by astronomers in the 19th century since the nebula looked like planets through their telescopes.

“When hydrogen and helium fuel that kept the star shining gets exhausted, the star expands in size and becomes a red giant star,” Rao explained. “Such stars shed most of their outer layers which expands outwards, and the inner core, made of carbon and oxygen, shrinks further and becomes hotter. This hot core shines brightly in the ultraviolet, and ionises the expanding gas. This glowing ionised gas is what is seen as a planetary nebula.”

Sriram Krishna, a student of Rao, spent many hours analysing the data from the Butterfly Nebula. “Its central star is one of the hottest that we know, at 220,000 degrees celsius. The name itself comes from the shape of the two lobes of expanding gas that look like the wings of a butterfly,” he said.

One might expect a planetary nebula to be spherical, but it actually exhibits a range of complicated structures. “We used the UVIT on AstroSat to make four images of the nebula, each in different ultraviolet ‘colours’, or filters. The image made with the filter centred at 160.8 nm, called F169M, had a surprise in store for us,” said Sriram.

Astronomers have studied the two lobes of the nebula for many years through visible light images. They expect that the more energetic ultraviolet light would be emitted closer to the central star, where the hot stellar wind hits the slowly expanding gas. “However, we discovered that the lobes imaged with the F169M filter in ultraviolet were about three times larger than the size of the lobes imaged in visible light,” according to Sriram. After careful analysis, their study concluded that this ultraviolet emission must be due to cold molecular hydrogen gas outside the visible lobes, which had gone undetected so far.

“Our discovery points to an unseen companion star in an orbit with the central star,” said Firoza Sutaria, one of the coauthors. In addition, researchers also discovered two faint jets blasting out from the centre at almost right angles to the new ultraviolet lobes.

The team led by Rao recently discovered a large ultraviolet halo in yet another planetary nebula using AstroSat, and will be looking at more such objects in the future. They hope that such discoveries may provide the answer to the age-old puzzle of the missing mass problem in planetary nebulae.

This discovery was made possible because of the uniqueness of UVIT. “Of all the ultraviolet telescopes in space, UVIT is special in its ability to image a large field of view with a very high resolution, or detail”, said V. Girish of ISRO.

“This ability, coupled with a novel image analysis software that we had developed, led us to this discovery”, explained Jayant Murthy, a coauthor of the paper and director of the Indian Institute of Astrophysics.

These results were accepted for publication in the journal Astronomy and Astrophysics on October 3, 2018.

The AstroSat Picture of the Month series, or APOM, is a year-old initiative of the Public Outreach and Education Committee of the Astronomical Society and the AstroSat Training and Outreach Team. The aim of APOM is to share the excitement of AstroSat science as well as the beauty of the universe with everyone. All APOMs are archived here.

 

[G10]

Astrosat is proving its mettle. Great thing coming out.

 

[darshan978]

ISRO's AstroSat Discovers Ultraviolet Wings on the Butterfly Nebula

https://thewire.in/the-sciences/isros-astrosat-discovers-ultraviolet-wings-on-the-butterfly-nebula

now imagine astrosat pointed toward earth haha... this is insane discoveries astrosat is making.. great job isro

 

[Indx TechStyle]

Oct 31, 2018
AstroSat Picture of the month - Oct 2018
Ultraviolet wings of the Butterfly Nebula

This month, APOM brings to you the ultraviolet view of one of the most spectacular objects in the sky, NGC 6302. Located nearly 3,800 light years away in the constellation Scorpius, NGC 6302 is a planetary nebula, whose shape is strikingly similar to the wings of a butterfly, hence aptly named as the Butterfly Nebula. This is the second planetary nebula that we bring forth to you, the first being NGC 40, covered in the APOM issue of December 2017.

Planetary nebulae are beautiful structures formed during the last few stages of the lives of stars like the Sun or a few times heavier. As the stars burn up all the hydrogen or helium fuel, they increase in size and become redder in colour, and are known as giant stars. As the giant star passes through few more stages, it continually sheds its outer layers revealing an inner hot core called the white dwarf. The white dwarf heats up the spewed-out gas which shines in the form of planetary nebula. Many of these planetary nebulae have strikingly symmetric shapes that need not be spherical and it has been suggested that this could be due to the various physical processes occurring in and around the star when it hurls out the gas from the outer layers. These nebulae are named planetary because when astronomers first observed them, they thought that these resembled planets. We now know that this is not the case, although the name has lingered.

Prof Kameshwar Rao, from the Indian Institute of Astrophysics (IIA), and his team have been investigating planetary nebulae in the ultraviolet light. They have imaged the Butterfly Nebula through the far and near-ultraviolet filters of the Ultraviolet Imaging Telescope (UVIT) of AstroSat. Using these images, they have discovered that gas which is bright in the far-ultraviolet extends beyond the known wings of the butterfly out to 5.5 light years from the centre, nearly three times of what is seen in the optical. The reddish coloured figure on the right is the far ultra-violet image of the Butterfly Nebula. The blue image is a cartoon that represents the full extent of the far-ultraviolet emission. These researchers argue that the extended far-ultraviolet light is due to cold hydrogen molecules in the gas present in the outer parts of the nebula which are excited by the central star. They suspect that these far-ultraviolet structures of the planetary nebula point to the possible presence of two central stars in a binary system that are gravitationally bound. The results have been published in the journal Astronomy & Astrophysics and the paper can be read here.

 

[Indx TechStyle]

https://arxiv.org/pdf/1810.02217.pdf

Amazing!!

 

[Aaj ka hero]

ISRO, NASA just spotted a black hole spinning so fast that it could be making space itself rotate

• India’s AstroSat and NASA’s Chandra X-Ray Observatory have confirmed the discovery of a black hole spinning close to the maximum possible speed.
• A black hole spinning that fast can make space itself rotate according to Einstein’s theory of relativity.
• This black hole is only one of five to have an accurately measured high spin rate.
• Researchers hypothesise that this could be the key to understanding how galaxies are formed.

Question-Who spotted First, asking it because... seems like astrosat first saw and Nasa then confirmed it.
Is this was the case?

 

[Indx TechStyle]

Question-Who spotted First, asking it because... seems like astrosat first saw and Nasa then confirmed it.
Is this was the case?

Can't say that but for spinning, I think only NASA is able to confirm that.

 

[Chinmoy]

Question-Who spotted First, asking it because... seems like astrosat first saw and Nasa then confirmed it.
Is this was the case?

Just read what is written.

India’s first dedicated astronomy satellite, the AstroSat spotted a black hole in the binary star system called 4U 1630-47 that’s spinning close to the maximum speed possible. NASA’s Chandra X-Ray Observatory confirmed the high spin rate.

Including the black hole discovered by the AstroSat, there are only five black holes have accurately measured high spin rates.

The black hole was discovered by ASTROSAT. Chandra observatory confirmed its presence.

 

[Indx TechStyle]

Nov 13, 2018
Announcement of Opportunity (AO) for Utilization of Astrosat Archival Data

AstroSat is India's first multi-wavelength observatory class mission. It completed three years of operations on 28th of September 2018. Data from AstroSat was opened to public on 26th September 2018
(https://www.isro.gov.in/update/26-sep-2018/archival-data-of-astrosat-released) and archived at ISSDC (https://astrobrowse.issdc.gov.in/astro.html).

Proposals are hereby invited from Astronomy community of the nation for utilizing AstroSat archival data. This announcement of opportunity (AO) is open to Indian scientific community for submitting research proposals towards utilisation of data from any and/or all the experiments for limited financial assistance. For a complete information of the AO please refer to AstroSat data AO.

The completely filled application has to reach [email protected] on or before 31-12-2018.

 

[Indx TechStyle]

Nov 30, 2018
AstroSat Picture of the Month Nov, 2018
Hot Ultraviolet stars in the Globular Cluster NGC 288

This month, APOM presents ultraviolet images of the globular cluster NGC 288, located at a distance of around 30,000 light years in the constellation Sculptor. This cluster was first described by John Dreyer in 1888. This is the second globular cluster in the APOM series, the first one being NGC 1851, presented a year ago. A globular cluster is a very large group of stars formed from the same cloud of gas and dust at nearly the same time. They are called globular because of the spherical distribution of stars, and each cluster is held together as a single entity by the gravity of the star members. Globular clusters are few of the oldest known objects in our galaxy. The stars in NGC 288 are believed to be nearly 12.6 billion years old.

The Ultraviolet Imaging Telescope (UVIT) on AstroSat has been used to image the stars in NGC 288 in the ultraviolet light, by a group of researchers from the Indian Institute of Astrophysics, Bangalore, and the National Research Council of Canada. The number of stars seen in the far-ultraviolet light are fewer than those seen in the near-ultraviolet light, and the reason for this is that only the hottest stars are seen in the far-ultraviolet.

Since globular clusters have very old stars, many of the heavier ones have already evolved to later phases of stellar lives (eg. red giant stars, horizontal branch stars). About 115 hot horizontal branch stars having surface temperature nearly twice that of the surface of Sun have been detected in NGC 288 using the near and far-ultraviolet filters of UVIT. A couple of very hot stars (extreme horizontal branch stars) whose whose surface temperatures are nearly five times that of the Solar surface have also been found. Using a combination of ultraviolet and optical light, these researchers have also identified 68 blue stragglers in this cluster. A blue straggler is a star formed when two stars either merge or transfer mass between them. Such stars have been mostly found in globular clusters where the star density is high. The capabilities of UVIT have made it easy for the researchers to see and inspect hot stars towards the cluster individually, allowing them to study the properties of each star, such as the mass and temperature.

The paper describing their results can be downloaded here.

Click here for the press story from India Science Wire and here for the entire APOM archive.

Courtesy: ISRO - Government of India

 

[Indx TechStyle]

AstroSat unravels how hot stars evolve in Globular Clusters in the Milky Way
Indian astronomers have peered deep into the Globular Cluster NGC 288, using the Ultraviolet Imaging Telescope (UVIT) on AstroSat to uncover the nature of special kinds of stars.

The image of this cluster is the AstroSat Picture of the Month for November. AstroSat is India's first dedicated multi-wavelength space observatory launched by the Indian Space Research Organisation in 2015.

Galaxies are made of innumerable stars, some of which are single, like our Sun while others are grouped together in clusters. Our Milky Way has over 150 Globular Clusters. These are clusters of hundreds of thousands of stars held together by their own gravity, packed into a size of only few tens of light years. They orbit the centre of the Milky Way as one unit. NGC 288, located around 30000 light years from the earth is one such Globular Cluster that was imaged by UVIT in three different 'ultraviolet colours'.

“Stars are not unchanging objects. They are born, they evolve through various stages of their life, and then they die,” explains Snehalata Sahu, a Ph.D. student at Bangalore-based Indian Institute of Astrophysics and lead author of research paper on NGC 288 published in Monthly Notices of the Royal Astronomical Society.

Stars of different masses go through different paths in their evolution. As they do so, their intrinsic luminosity as well as their surface temperature (and hence colour) changes in different ways depending on their mass. Astronomers name different types of stars which are in various phases of their evolution, by their location in this luminosity versus temperature plot. This study has thrown up interesting results for two such kinds of stars, the Blue Horizontal Branch (BHB) stars and the Blue Straggler (BS) stars in the cluster NGC 288.

The picture of NGC 288 in the optical (left side; credit: ESO/DSS) shows numerous sun-like cooler stars and it is hard to locate hot stars. The image of the same cluster in the ultraviolet (right side, taken by UVIT, yellow is the near-UV and white is the far-UV image; credit: Snehalata Sahu) shows only hot stars as the cooler stars become undetectable.

" Stars are not unchanging objects. They are born, they evolve through various stages of their life, and then they die " : Snehalata Sahu
All stars in a Globular Cluster are born together, and are of the same age. They are also about the same distance from us. “Hotter stars are bluer and are bright in the ultraviolet (UV), where they are best studied,” said Professor Annapurni Subramaniam, a co-author of the paper.

UVIT has the unique capability of imaging a large field of view with high resolution. “This helped us not only image the entire cluster up to its outer most regions but also isolate every individual hot star even in the crowded centre of the cluster,” she added. This gave researchers advantage over previous ultraviolet studies of such clusters. They could measure near-UV and far-UV brightness of 115 HB stars, 68 BS stars and 2 Extreme HB (EHB) stars in NGC 288. Combining this data with already known optical properties of these stars, they could accurately model each of these UV-bright stars individually, and derive their temperatures as well.

“We first looked at the UV properties of the bluer HB stars and could easily distinguish between those stars cooler than 11500 degrees and those that are hotter,” said Sahu. “This change in stellar properties at 11500 degrees is due to atomic diffusion, which alters chemical make-up of outer layers of the star. We have now shown that this break can be easily identified from ultraviolet measurements of these stars and this method can now be used for other clusters as well.”

Professor Kameswara Rao, a co-author of the study, explained that the team could calculate the mass and size of the EHB stars as well. “We were able to identify these as sub-dwarf stars, about five times smaller than our Sun, but more than five times hotter. This was possible mainly because we could measure their ultraviolet properties”.

The location of stars within a globular cluster changes with time as heavier ones settle into the centre. Blue Straggler or BS stars are interesting in themselves. In crowded centres of Globular Clusters, some stars swallow matter from a companion star and sometimes two stars merge to form a new one too. Astronomers believe that BS stars are formed this way, and that’s why their ultraviolet properties are so different. By calculating the mass of each BS star from their ultraviolet data, and by studying their locations in the cluster, researchers could infer the nature of the motion of the stars within the cluster, otherwise known as its dynamical age.

“We have now shown that ultraviolet imaging of Globular Clusters is the easiest and clearest way to study the properties of some of these hot stars with peculiar properties. The superior resolution and large field of view of UVIT will prove crucial in understanding the evolution of these kinds of stars,” said Rao.

The study was conducted by Snehalata Sahu, Annapurni Subramaniam and Kameswara Rao from the Indian Institute of Astrophysics, along with Patrick Cote and Peter Stetson from the National Research Council of Canada.

AstroSat Pictures of the Month (APOM) is a joint initiative of the Public Outreach and Education Committee (POEC) of the Astronomical Society of India and AstroSat Training and Outreach Team. APOM helps in bringing higher energy sky seen by AstroSat closer to people through images. All APOMs are archived at click here India Science Wire.

Source: vigyanprasar.gov.in

 

[Indx TechStyle]

APOM Archives - The Public Outreach & Education Committee of the Astronomical Society of India

 

[Indx TechStyle]

Jan 31, 2019
AstroSat Picture of the Month of Jan, 2019

The 97 minute orbit of AstroSat around the Earth. The orbit is roughly equatorial (top right), inclined at around 6 degrees to it (top left). This results in each orbit being slightly displaced from the previous one (bottom). Pic Credits: Leo Jackson John, Operation Director, AstroSat, ISTRAC, ISRO

When seeing images from AstroSat, have you ever wondered where exactly is the satellite, how does it move, and how do astronomers get their hands on the data? This month's APOM is here to answer those questions for you.

AstroSat was launched by ISRO on 28 September, 2015 from Sriharikota https://www.isro.gov.in/about-isro/satish-dhawan-space-centre-sdsc-shar, on board the PSLV-C30 into its current orbit. This is a low-earth equatorial orbit, at a height of 650 km above the Earth. This orbit is not exactly over the equator, but is inclined at angle of about 6 degree to it. In the top left image, the green line marks the equator and the yellow line marks the orbit of AstroSat and the top right image is a view from over the north pole. But why was this orbit chosen?

Our Earth has a magnetic field (https://en.wikipedia.org/wiki/Earth's_magnetic_field), which behaves overall like a bar magnet (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/MagEarth.html), with its poles a few degrees from the poles defined by our rotation. These magnetic fields trap charged particles within them, which form the Van Allen belts (https://www.space.com/33948-van-allen-radiation-belts.html). These belts are much closer to the Earth over the southern Atlantic Ocean. An equatorial orbit reduces the effect of this South Atlantic Anomaly https://en.wikipedia.org/wiki/South_Atlantic_Anomaly, on AstroSat which carries very sensitive instruments. Making the inclination exactly zero requires more resources and hence a 6 degree inclination was chosen.

AstroSat takes about 97 minutes to orbit the Earth once. Hence, it will not pass directly overhead the same point in successive orbits. Each orbit, therefore, will be slightly shifted with respect to the previous one. The individual orbits shown in red in the bottom image mark orbits. One orbit per week is plotted for clarity. Data is beamed down from an antenna on the satellite once every orbit, when it passes over India. The data is received by ISRO's dedicated Indian Deep Space Network http://isrohq.vssc.gov.in/VSSC_V4/index.php/ground-segment/82-chandrayaa... antenna in Byalalu https://en.wikipedia.org/wiki/Indian_Deep_Space_Networknear Bengaluru (marked as BLR). All orbits of AstroSat fall within the visibility of this antenna, which is marked by a circle centred at Byalalu. ISRO can also use an antenna in Indonesia, marked BIK, to monitor the satellite when needed. All the command, control and tracking of AstroSat is done by ISTRAC https://www.isro.gov.in/about-isro/isro-telemetry-tracking-and-command-n... in Bengaluru.

As of 30 January 2019, AstroSat has completed more than 18,000 orbits around the Earth, acting as our high energy eye, uncovering the nature of neutron stars, black holes, hot star, and many strange celestial objects. May it continue to do so for many more orbits!

 

[Raweg]

Jan 31, 2019
AstroSat Picture of the Month of Jan, 2019

The 97 minute orbit of AstroSat around the Earth. The orbit is roughly equatorial (top right), inclined at around 6 degrees to it (top left). This results in each orbit being slightly displaced from the previous one (bottom). Pic Credits: Leo Jackson John, Operation Director, AstroSat, ISTRAC, ISRO

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