Vampire stars, known as blue straggler stars (BSS), defy simple models of stellar evolution and show many characteristics of younger stars. Photo: PIB

Team of astronomers from the Indian Institute of Astrophysics (IIA) have made the discovery that a vampire star has been rejuvenating its youth by sucking up material from a companion in the star cluster M67 located in the constellation Cancer.

Vampire stars, known as blue straggler stars (BSS), defy simple models of stellar evolution and show many characteristics of younger stars.

“This anomalous youth is explained theoretically as due to rejuvenation by eating up material from a binary stellar companion. Star clusters are useful test-beds to test this theory as they host a large number of binary stars, some of which can lead to the formation of vampire stars. Once rejuvenated, these stars follow a different path of evolution when compared to Sun-like single stars. So far, detection of sucked up material along with the sighting of their remnant binary companion was elusive,” said the department of science and technology.

However, recently, a team of astronomers from IIA made a groundbreaking discovery of a vampire star in M67, that sheds light on a complex rejuvenation process, known as mass-transfer in a binary system.

The key to this detection was data from the UltraViolet Imaging Telescope, on board AstroSat, India’s first dedicated space observatory.

The scientists studied the surface composition of the vampire star in M67, called WOCS 9005, using spectroscopy, a technique where the light of the star is dispersed into its colors like the rainbow.

“This star is expected to show chemistry very similar to our Sun, but we found that its atmosphere is rich in heavy elements such as barium, yttrium, and lanthanum”, said Harshit Pal, the lead author of the paper.

“The presence of heavy elements in the spectrum pointed to a polluted atmosphere of the vampire star and the source of pollution being an external source. The external source is likely to be its binary companion, which must have made the heavy elements when it passed through its AGB phase, and later became a white dwarf star”, said Prof. Annapurni Subramaniam, co-author of the paper and Director IIA.

Prof. Subramaniam added that the blue straggler star that we see now must have eaten up most of this barium-rich material due to its gravitational pull, and is now presenting itself as a rejuvenated star.

While moving in its orbit roughly once a month, the moon will occasionally occult, or hide, bright stars that are behind, and sometimes, even planets. 
| Photo Credit: AP

The Bengaluru-based Indian Institute of Astrophysics (IIA) has filmed the passing of the moon in front of Antares, a bright red star.

The moon passed in front of Antares on April 27, hiding it for roughly 40 minutes. IIA said that this event was visible only from southern India. IIA filmed the event from its Bengaluru campus using a camera on an 8-inch telescope.

While moving in its orbit roughly once a month, the moon will occasionally occult, or hide, bright stars that are behind, and sometimes, even planets. This happens now and then for the star Antares (Jyeshtha), which is the brightest star in the constellation of Scorpius. Since the moon is relatively close to the Earth, such occultations will be visible only from some locations on the globe, similar to why a solar eclipse is seen only from a particular part of the globe.

The last such occultation of Antares, which was visible from India, was on February 5 this year. The next one will be in June 2027. However, the occultation of the planet Saturn by the moon can be seen from India on July 24, and again on October 14 in 2024.

As seen from Bengaluru, Antares disappeared behind the bright side of the gibbous moon around 1.13 a.m. and reappeared at the darker side around 1.53 a.m. IIA has a video of the disappearance and reappearance. In the videos, the telescope is tracking Antares, and the relative motion of the moon is also clearly visible. The shaking of the image is due to winds buffeting the telescope, and the shimmering of the image is due to the Earth’s atmosphere.

A long-exposure photograph of stars over the Hanle Dark Sky Reserve in Ladakh.
| Photo Credit: Akash Anandh

The temperatures were subzero and freezing. The conditions were unforgiving. We were elated and thrilled being outdoors all night.

At 4,300 metres above sea level, we felt it could have been the Everest Base Camp. In reality, we were at Hanle, in the Union Territory of Ladakh. The air is so thin at such altitudes that the oxygen level is less than 60% of what one is normally used to at sea level. Before getting here, we had to acclimatise ourselves for 48 hours at Leh, at an altitude of 3,500 m, before climbing up to Hanle.

It is definitely not for everyone. But it was certainly for us: we were a group of amateur astronomers invited by the Indian Institute of Astrophysics (IIA) to attend the HDSR Star Party 2023, organised and conducted by IIA.

The Hanle Dark Sky Reserve (HDSR) is India’s first dark sky region, and is centred at Hanle in Eastern Ladakh, around the Indian Astronomical Observatory. HDSR preserves the dark skies by reducing light pollution in the surrounding areas, and uses these dark skies to promote astrotourism as a means to further enhance socio-economic development in the area.

Seeing into dark skies

A dark sky is the night sky as nature meant for it to be: without any light pollution. Light from the human-made objects that we use – especially outdoor lighting sources – blocks our view of the stars and most celestial objects in the night sky.

Ironically, a dark sky lets you see better. From within a light-polluted city, we can typically see only a handful of stars. But from a dark site, we can see thousands in the same location of the sky.

Apart from stars, the Milky Way’s galactic centre and its arms are clearly visible to the naked eye. We can also see several star clusters, nebulae, galaxies such as the Andromeda and the Triangulum.

Zodiacal light – a faint glow of diffuse sunlight scattered by interplanetary dust in the Solar System; airglow – an optical phenomenon caused by faint emission of light in the earth’s atmosphere; and gegenschein – a bright spot in the night sky centred at the antisolar point, caused due to backscatter of sunlight by interplanetary dust – are also visible.

Venus can be so bright in the night sky that its light can cast shadows on the ground, just as moonlight does.

A start to something big

Although some of us astrophotographers were aware of the theories of these optical phenomena and the fact that we could see so many stars and celestial objects under the darkest of skies, it was still an overwhelming feeling to actually observe and experience them under the Bortle Class 1 skies of Hanle.

The Bortle Scale helps amateur astronomers measure the night sky’s brightness at a given location. The scale ranges from Class 1, the darkest skies available over the earth, through to Class 9, which denotes the pale, light-marred skies over the insides of cities.

A sense of thrill as well as caution filled the thin air under the dark skies of Hanle. Observing outdoors in these harsh conditions – with or without equipment – meant one had to be both strong-willed and careful. But it was worth every second as caution soon led to exhilaration and then wonder.

For us amateur astronomers, the three nights and days of the HDSR Star Party made for a great opportunity to observe under pristine night skies. We could also connect with fellow amateur astronomers who had come from various parts of the country: they were experienced amateurs as well as young ones with starlit eyes.

We also got to rub shoulders with professional astronomers, exchanging ideas and information on all things astronomy, including the particulars of visual observation and the techniques of astrophotography, as well as share large telescopes and imaging equipment during the event. In all, it was an unforgettable experience.

Being the first ever dark sky reserve in the country, HDSR is certainly a source of pride for India and will be a blueprint for other dark sites in other regions. And just like at Hanle, upcoming dark sky reserves can also promote astrotourism, which will help both amateur astronomers like us as well as local communities.

The Star Party is also highly likely to evolve into an annual event, and I am glad that I was part of the successful first edition of the HDSR Star Party this year. It was expertly and thoughtfully planned and conducted by Dorje Angchuk, who is the engineer-in-charge at the Indian Astronomical Observatory in Hanle, and Niruj Mohan Ramanujam, head of the IIA SCOPE Section.

I believe the event was a great start to something big for casual stargazers, passionate amateur astronomers, and our space-loving country as a whole.

(Akash Anandh is an amateur astronomer, astrophotographer, writer, and science communicator)

akash.anandh@gmail.com