First polluted white dwarf found in Gaia DR2

July 4, 2018 by Tomasz Nowakowski, Phys.org report
KAST spectra of GaiaJ1738−0826 (black curve) with model having the specified parameters overlaid (red line). Credit: Melis et al., 2018.

Astronomers have identified the first metal-polluted white dwarf star from the Gaia Data Release 2 (DR2) provided by ESA's Gaia satellite. The newly found star received designation GaiaJ1738−0826. The finding is detailed in a paper published June 24 on the arXiv pre-print repository.

DR2, published on April 25, provides high-precision measurements, including positions in the sky, parallaxes and proper motions for more than 1 billion sources in our galaxy. The release contains observational data collected by Gaia in the timespan of nearly two years – between July 25, 2014 and May 23, 2016.

Now, a team of astronomers led by Carl Melis of the University of California San Diego, has conducted spectroscopic observations of one white dwarf listed in the DR2 catalog. They employed the KAST spectrograph mounted on the Shane 3-m telescope at Lick Observatory in California to characterize this white dwarf. They found that this star exhibits strong absorption line of ionized calcium.

"We present the first metal-polluted single white dwarf (WD) star identified through Gaia DR2 (Brown et al. 2018). GaiaJ1738−0826 was discovered to have strong Ca II absorption in initial spectroscopic characterization at Lick Observatory," the astronomers wrote in the paper.

Observations conducted by Melis' team indicate that GaiaJ1738−0826 is a metal-polluted with a radius of 0.012 solar radii and a mass of 0.6 solar masses. It has an effective temperature of 7,050 K, luminosity of 3.3 percent of that of our sun and an estimated cooling time of about 1.7 billion years.

Furthermore, the researchers calculated that GaiaJ1738−0826 has a calcium mass accretion rate in steady-state of approximately 2,600 kilograms per second. This value indicates that GaiaJ1738−0826 could be accreting 160,000 kilograms every second, assuming that calcium makes up about 1.6 percent of the total heavy element accretion rate in this white dwarf.

The authors of the paper noted that the accreting rate at a level of 160,000 kilograms per second could indicate the presence of a circumstellar accretion disk around GaiaJ1738−0826. However, archival data from the VISTA Hemisphere Survey and NASA's Spitzer space telescope do not confirm this assumption.

According to the paper, GaiaJ1738−0826 resembles the first confirmed white dwarf of DAZ-type (displaying absorption features also from heavier elements), known as G 74−7. This DAZ white dwarf is similar in size, mass, luminosity, effective temperature and cooling time to GaiaJ1738−0826. It's calcium mass accretion rate was found to be at a level of around 1,500 kilograms per second.

"Notably, GaiaJ1738−0826 resembles in many ways the first confirmed metal-polluted hydrogen atmosphere WD, the DAZ G 74−7 (Lacombe et al. 1983)," the paper reads.

The researchers concluded that polluted like GaiaJ1738−0826 offer a glimpse into the fate of planetary systems and an unparalleled method of determining the composition of solid material in planetary systems. Moreover, such have been recently found very helpful in providing structural information for massive, differentiated rocky bodies.

Explore further: Caffau's star is a dwarf, Gaia DR2 confirms

More information: The first polluted white dwarf from Gaia DR2: the cool DAZ GaiaJ1738-0826, arXiv:1806.09056 [astro-ph.SR] arxiv.org/abs/1806.09056

Abstract
We present the first metal-polluted single white dwarf star identified through Gaia DR2. GaiaJ1738-0826, selected from color and absolute magnitude cuts in the Gaia DR2 data, was discovered to have strong Ca~II absorption in initial spectroscopic characterization at Lick Observatory. Notably, GaiaJ1738-0826 resembles in many ways the first confirmed metal-polluted hydrogen atmosphere white dwarf, the DAZ G74-7.

Related Stories

Caffau's star is a dwarf, Gaia DR2 confirms

May 7, 2018

Caffau's star, the most metal-poor object known to date and one of the oldest stars in the Milky Way galaxy, turns out to be a dwarf star, according to an analysis of new measurements provided by Gaia Data Release 2 (DR2). ...

Astronomers observe huge flares on a young brown dwarf

June 6, 2018

Using Kepler, astronomers have spotted two superflares on a very young brown dwarf known as CFHT-BD-Tau 4. The two superflares turn out to be the strongest flares observed on any brown dwarf so far. The finding is detailed ...

Powerful flare detected on an M-dwarf star

April 25, 2018

An international team of astronomers reports the finding of ASASSN-18di—a powerful white-light superflare on a previously undetected, mid-type M-dwarf star. The discovery is detailed in a paper published April 12 on the ...

Recommended for you

Exoplanet stepping stones

November 20, 2018

Astronomers have gleaned some of the best data yet on the composition of a planet known as HR 8799c—a young giant gas planet about 7 times the mass of Jupiter that orbits its star every 200 years.

Encouraging prospects for moon hunters

November 20, 2018

Astrophysicists of the University of Zürich, ETH Zürich and the NCCR PlanetS show how the icy moons of Uranus were born. Their result suggests that such potentially habitable worlds are much more abundant in the Universe ...

Gravitationally lensed quasars

November 19, 2018

The path of light is bent by mass, an effect predicted by Einstein's theory of gravity, and when a massive galaxy or cluster lies along our line-of-sight to a more distant galaxy its matter will act as a lens to image the ...

6 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Benni
2.6 / 5 (5) Jul 04, 2018
"......the first metal-polluted white dwarf star...."

shame on us
rrwillsj
1 / 5 (3) Jul 04, 2018
right benni. (does that qualify as an oxymoron?)

If we close our eyes tightly and plug our ears and loudly warble La-La-La the pollution does not exist.

So it's not our fault and you can't blame us. And we won't have to take any responsibility for causing said pollution.
joel in oakland
5 / 5 (1) Jul 04, 2018
"Polluted"? I was hoping for an explanation. Why that word?
Benni
2.3 / 5 (3) Jul 04, 2018
"Polluted"? I was hoping for an explanation. Why that word?


oxymoron for: HUMAN
Edenlegaia
4.5 / 5 (2) Jul 05, 2018
....since when are we responsible for every kind of "pollution" out there, assuming it would really be pollution?
torbjorn_b_g_larsson
5 / 5 (2) Jul 05, 2018
It is a synonym to "contamination", which is a term for that something that should be clean (hydrogen atmosphere of a white dwarf) is not (" a calcium mass accretion").

The press release is purely technical unfortunately. But the context seems to be that some white dwarfs show signs of having recently ingested planetary bodies that survived the change from main star over red giant to white dwarf and *then* fell onto the star. The "metal" atoms takes a while to sink into the star and disappear from the spectra.

"The researchers concluded that polluted white dwarfs like GaiaJ1738−0826 offer a glimpse into the fate of planetary systems and an unparalleled method of determining the composition of solid material in planetary systems. Moreover, such stars have been recently found very helpful in providing structural information for massive, differentiated rocky bodies."

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.