A New Class of Variable Stars Revealed

Feb 26, 2010

(PhysOrg.com) -- Modern astronomy sometimes makes discoveries by looking in new places, the distant universe for example, using telescopes and instruments that extend the previous limits of detection.

But sometimes new discoveries can come from applying modern technologies to the task of more carefully examining conventional data.

The Harvard College Observatory maintains a collection of more than 500,000 glass photographic plates of the sky taken over a century - from between about 1880 and 1980. They constitute the only continuous record of the whole sky in existence for this period, with every point on the sky having been observed between 500 and 1000 times.

The Digital Access to a Sky Century at Harvard (DASCH) is a project now underway to digitize all of these plates and search for changes. In one of the first results of this ongoing program, a new class of variable has been discovered.

Variable stars are stars that change in brightness. They can do so for many reasons, from explosions as to pulsations in their atmospheres to eclipses in binary star systems. Sometimes the changes are periodic and other times erratic, but by far most known variable stars change noticeably in short times - over time scales of less than a year. Variable stars came as quite a shock when they were discovered in the early 1600's because people thought that the stars were cosmic constants, but today variable stars seem rather matter-of-course.

CfA astronomers Sumin Tang, Jonathan Grindlay, and Edward Los, together with a colleague, used the first results of the DASCH project to discover three objects in what appears to be a new class of variable stars that change in optical brightness (both dimming and brightening) by more than a factor of two over a timescale of 10-100 years.

This kind of variation has never been seen before; imagine if the sun were to vary in brightness by a factor of two in a century!

The astronomers use follow-up spectroscopic observations to report that the three stars are similar to one another, and are slightly less massive and older than the sun.

They suggest that the cause of variability could be related to the production of dust, or perhaps involve changes in the nuclear reactions underway. Once DASCH has found other stars of this type, and more detailed follow-up studies can be be undertaken, this new kind of variable star can add the details of its aging personality to our understanding of what happens as stars evolve.

Explore further: Image: NGC 6872 in the constellation of Pavo

Related Stories

Symbiotic Stars

Feb 22, 2010

(PhysOrg.com) -- Many, perhaps even most stars, are members of binaries -- two stars that orbit each other. Symbiotic stars are a small subset of binaries with an attitude: they display characteristic, dramatic, ...

Building a stellar time machine

Jul 07, 2009

(PhysOrg.com) -- Harvard researchers are building a celestial time machine that lets astronomers look back at hundreds of thousands of objects in the Earth’s skies over the past century.

Cepheids and their 'cocoons'

Feb 28, 2006

Using ESO's Very Large Telescope Interferometer (VLTI) at Cerro Paranal, Chile, and the CHARA Interferometer at Mount Wilson, California, a team of French and North American astronomers has discovered envelopes ...

Turbulence May Promote the Birth of Massive Stars

Feb 23, 2009

(PhysOrg.com) -- On long, dark winter nights, the constellation of Orion the Hunter dominates the sky. Within the Hunter's sword, the Orion Nebula swaddles a cluster of newborn stars called the Trapezium. These stars are ...

Recommended for you

Image: NGC 6872 in the constellation of Pavo

7 hours ago

This picture, taken by the NASA/ESA Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2), shows a galaxy known as NGC 6872 in the constellation of Pavo (The Peacock). Its unusual shape is caused ...

Measuring the proper motion of a galaxy

8 hours ago

The motion of a star relative to us can be determined by measuring two quantities, radial motion and proper motion. Radial motion is the motion of a star along our line of sight. That is, motion directly ...

Gravitational waves according to Planck

Sep 22, 2014

Scientists of the Planck collaboration, and in particular the Trieste team, have conducted a series of in-depth checks on the discovery recently publicized by the Antarctic Observatory, which announced last ...

Infant solar system shows signs of windy weather

Sep 22, 2014

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have observed what may be the first-ever signs of windy weather around a T Tauri star, an infant analog of our own Sun. This may help ...

Finding hints of gravitational waves in the stars

Sep 22, 2014

Scientists have shown how gravitational waves—invisible ripples in the fabric of space and time that propagate through the universe—might be "seen" by looking at the stars. The new model proposes that ...

How gamma ray telescopes work

Sep 22, 2014

Yesterday I talked about the detection of gamma ray bursts, intense blasts of gamma rays that occasionally appear in distant galaxies. Gamma ray bursts were only detected when gamma ray satellites were put ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

yyz
not rated yet Feb 26, 2010
This just goes to show how archival plate collections, properly managed and scanned into the digital age, can be an immense treasure trove of information. IIRC, a young Bradley Schaefer first looked for optical images (by light-table blink comparators) of gamma-ray bursters using the HCO photographic archives.
in7x
not rated yet Feb 26, 2010
I hope they stick with the research on this particular object and better define the cause of variability.

*waves hand* Must be dust!
yyz
not rated yet Feb 26, 2010
I can remember one of Dr. Scheafer's papers actively discussing the possibility of "firefly' emission on several of the Harvard plates. No stone was left unturned.