Andrew Yee[_1_]
February 12th 08, 11:27 PM
ESO Education and Public Relations Dept.
----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/public/outreach/press-rel/pr-2008/pr-05-08.html
----------------------------------------------------------------------------
Science Contact:
Pierre Kervella
Observatoire de Paris-Meudon, France
Phone: +33 1 45 07 79 66
Embargoed till 11 February 2008, 00:01 GMT
ESO Science Release 05/08
Light echoes whisper the distance to a star
Astronomers calibrate the distance scale of the Universe
Taking advantage of the presence of light echoes, a team of astronomers have
used an ESO telescope to measure, at the 1% precision level, the distance of
a Cepheid -- a class of variable stars that constitutes one of the first
steps in the cosmic distance ladder.
"Our measurements with ESO's New Technology Telescope at La Silla allow us
to obtain the most accurate distance to a Cepheid," says Pierre Kervella,
lead-author of the paper reporting the result.
Cepheids [1] are pulsating stars that have been used as distance indicators
since almost a hundred years. The new accurate measurement is important as,
contrary to many others, it is purely geometrical and does not rely on
hypotheses about the physics at play in the stars themselves.
The team of astronomers studied RS Pup, a bright Cepheid star located
towards the constellation of Puppis ('the Stern') and easily visible with
binoculars. RS Pup varies in brightness by almost a factor of five every
41.4 days. It is 10 times more massive than the Sun, 200 times larger, and
on average 15 000 times more luminous.
RS Pup is the only Cepheid to be embedded in a large nebula [2], which is
made of very fine dust that reflects some of the light emitted by the star.
Because the luminosity of the star changes in a very distinctive pattern,
the presence of the nebula allows the astronomers to see light echoes and
use them to measure the distance of the star.
"The light that travelled from the star to a dust grain and then to the
telescope arrives a bit later than the light that comes directly from the
star to the telescope," explains Kervella. "As a consequence, if we measure
the brightness of a particular, isolated dust blob in the nebula, we will
obtain a brightness curve that has the same shape as the variation of the
Cepheid, but shifted in time."
This delay is called a 'light echo', by analogy with the more traditional
echo, the reflection of sound by, for example, the bottom of a well.
By monitoring the evolution of the brightness of the blobs in the nebula,
the astronomers can derive their distance from the star: it is simply the
measured delay in time, multiplied by the velocity of light (300 000 km/s).
Knowing this distance and the apparent separation on the sky between the
star and the blob, one can compute the distance of RS Pup.
From the observations of the echoes on several nebular features, the
distance of RS Pup was found to be 6500 light years, plus or minus 90 light
years.
"Knowing the distance to a Cepheid star with such an accuracy proves crucial
to the calibration of the period-luminosity relation of this class of
stars," says Kervella. "This relation is indeed at the basis of the distance
determination of galaxies using Cepheids."
RS Pup is thus distant by about a quarter of the distance between the Sun
and the Centre of the Milky Way. RS Pup is located within the Galactic
plane, in a very populated region of our Galaxy.
More Information
"The long-period Galactic Cepheid RS Puppis - I. A geometric distance from
its light echoes", P. Kervella et al. is in press in Astronomy and
Astrophysics.
The team is composed of Pierre Kervella and Guy Perrin (LESIA, Observatoire
de Paris, France), Antoine Merand (Center for High Angular Resolution
Astronomy, Atlanta, Georgia, USA), Laszlo Szabados (Konkoly Observatory,
Budapest, Hungary), Pascal Fouque (Observatoire Midi-Pyrenees, Toulouse,
France), David Bersier (Liverpool John Moores University, UK), and Emanuela
Pompei (ESO).
Notes
[1]: Cepheids are rare and very luminous pulsating stars whose luminosity
varies in a very regular way. They are named after the star Delta Cephei in
the constellation of Cepheus, the first known variable star of this
particular type and bright enough to be easily seen with the unaided eye.
Almost a century ago, in 1912, American astronomer Henrietta Leavitt
published a relation between the intrinsic brightness and the pulsation
period of Cepheids, the longer periods corresponding to the brighter stars.
This relation still plays today a central role in the extragalactic distance
scale.
[2]: The nebula around RS Pup was discovered in 1961 by Swedish astronomer
Bengt Westerlund, who later became ESO Director in Chile (1970-74). Shortly
after, in 1972, the American astronomer Robert Havlen, then visiting ESO
Chile, published the first study of the nebula in the then rather young
European journal Astronomy & Astrophysics.
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Czech Republic: Pavel Suchan, +420 267 103 040
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vornle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Spain: Dr. Miguel Mas-Hesse, +34918131196
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
USA: Dr. Paola Rebusco, +1-617-308-2397
----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------
----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/public/outreach/press-rel/pr-2008/pr-05-08.html
----------------------------------------------------------------------------
Science Contact:
Pierre Kervella
Observatoire de Paris-Meudon, France
Phone: +33 1 45 07 79 66
Embargoed till 11 February 2008, 00:01 GMT
ESO Science Release 05/08
Light echoes whisper the distance to a star
Astronomers calibrate the distance scale of the Universe
Taking advantage of the presence of light echoes, a team of astronomers have
used an ESO telescope to measure, at the 1% precision level, the distance of
a Cepheid -- a class of variable stars that constitutes one of the first
steps in the cosmic distance ladder.
"Our measurements with ESO's New Technology Telescope at La Silla allow us
to obtain the most accurate distance to a Cepheid," says Pierre Kervella,
lead-author of the paper reporting the result.
Cepheids [1] are pulsating stars that have been used as distance indicators
since almost a hundred years. The new accurate measurement is important as,
contrary to many others, it is purely geometrical and does not rely on
hypotheses about the physics at play in the stars themselves.
The team of astronomers studied RS Pup, a bright Cepheid star located
towards the constellation of Puppis ('the Stern') and easily visible with
binoculars. RS Pup varies in brightness by almost a factor of five every
41.4 days. It is 10 times more massive than the Sun, 200 times larger, and
on average 15 000 times more luminous.
RS Pup is the only Cepheid to be embedded in a large nebula [2], which is
made of very fine dust that reflects some of the light emitted by the star.
Because the luminosity of the star changes in a very distinctive pattern,
the presence of the nebula allows the astronomers to see light echoes and
use them to measure the distance of the star.
"The light that travelled from the star to a dust grain and then to the
telescope arrives a bit later than the light that comes directly from the
star to the telescope," explains Kervella. "As a consequence, if we measure
the brightness of a particular, isolated dust blob in the nebula, we will
obtain a brightness curve that has the same shape as the variation of the
Cepheid, but shifted in time."
This delay is called a 'light echo', by analogy with the more traditional
echo, the reflection of sound by, for example, the bottom of a well.
By monitoring the evolution of the brightness of the blobs in the nebula,
the astronomers can derive their distance from the star: it is simply the
measured delay in time, multiplied by the velocity of light (300 000 km/s).
Knowing this distance and the apparent separation on the sky between the
star and the blob, one can compute the distance of RS Pup.
From the observations of the echoes on several nebular features, the
distance of RS Pup was found to be 6500 light years, plus or minus 90 light
years.
"Knowing the distance to a Cepheid star with such an accuracy proves crucial
to the calibration of the period-luminosity relation of this class of
stars," says Kervella. "This relation is indeed at the basis of the distance
determination of galaxies using Cepheids."
RS Pup is thus distant by about a quarter of the distance between the Sun
and the Centre of the Milky Way. RS Pup is located within the Galactic
plane, in a very populated region of our Galaxy.
More Information
"The long-period Galactic Cepheid RS Puppis - I. A geometric distance from
its light echoes", P. Kervella et al. is in press in Astronomy and
Astrophysics.
The team is composed of Pierre Kervella and Guy Perrin (LESIA, Observatoire
de Paris, France), Antoine Merand (Center for High Angular Resolution
Astronomy, Atlanta, Georgia, USA), Laszlo Szabados (Konkoly Observatory,
Budapest, Hungary), Pascal Fouque (Observatoire Midi-Pyrenees, Toulouse,
France), David Bersier (Liverpool John Moores University, UK), and Emanuela
Pompei (ESO).
Notes
[1]: Cepheids are rare and very luminous pulsating stars whose luminosity
varies in a very regular way. They are named after the star Delta Cephei in
the constellation of Cepheus, the first known variable star of this
particular type and bright enough to be easily seen with the unaided eye.
Almost a century ago, in 1912, American astronomer Henrietta Leavitt
published a relation between the intrinsic brightness and the pulsation
period of Cepheids, the longer periods corresponding to the brighter stars.
This relation still plays today a central role in the extragalactic distance
scale.
[2]: The nebula around RS Pup was discovered in 1961 by Swedish astronomer
Bengt Westerlund, who later became ESO Director in Chile (1970-74). Shortly
after, in 1972, the American astronomer Robert Havlen, then visiting ESO
Chile, published the first study of the nebula in the then rather young
European journal Astronomy & Astrophysics.
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Czech Republic: Pavel Suchan, +420 267 103 040
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vornle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Spain: Dr. Miguel Mas-Hesse, +34918131196
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
USA: Dr. Paola Rebusco, +1-617-308-2397
----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------