Andrew Yee[_1_]
June 7th 07, 12:50 AM
Institute for Astronomy
University of Hawai'i
Director's Office
2680 Woodlawn Drive, Honolulu, Hawaii 96822
(808) 956-8566 Fax: (808) 946-3467
Website: http://www.ifa.hawaii.edu
CONTACT:
Dr. Rolf-Peter Kudritzki (808) 956-8566 or Mrs. Karen Rehbock (808) 956-6829
FOR RELEASE: 2:30 p.m. Hawaiian Standard Time, May 28, 2007
ASTRONOMERS FIND NEW WAY TO MEASURE DISTANCE TO OTHER GALAXIES
Dr. Rolf-Peter Kudritzki of the Institute for Astronomy (IfA) at the
University of Hawaii at Manoa will report today on a new method used to
measure extragalactic distances accurately based on the stellar gravities
and effective temperatures of blue supergiant stars in galaxies beyond the
Local Group. The paper will be presented at the meeting of the American
Astronomical Society (AAS) in Honolulu. His collaborators for this project
are Drs. Fabio Bresolin and Miguel Urbaneja (IfA) and a group of astronomers
of the Universidad de Concepcion, Chile, led by Dr. Wolfgang Gieren.
Kudritzki and his collaborators observed the galaxy NGC 300, which is about
6 million light-years away and located in the constellation Sculptor, to
test this new method of measuring distances between galaxies. They took
spectra to measure the atmospheric temperature of the stars and their
surface gravity. With these measurements, they were able to determine the
intrinsic brightness of each star and then to compare the apparent
brightness with intrinsic brightness to find the distance.
They then compared their distance measurements to those made using Cepheid
variable stars, the traditional way to measure the distance to nearby
galaxies. "This new method works excitingly well," says Kudritzki. "It seems
that we can determine distances to other galaxies with an accuracy of five
percent, which opens a complementary way to constrain the Hubble constant
more precisely." The Hubble constant denotes the current rate of expansion
of the universe.
Their observations consisted of medium- and low-resolution spectra taken
with the Focal Reducer Spectrograph (FORS) on the European Southern
Observatory's Very Large Telescope in Paranal, Chile. Kudritzki was
instrumental in designing FORS while at the University of Munich before
coming to Hawaii in 2000. In its most recent work on other galaxies, the
project team has also used the Low Resolution Imaging Spectrometer (LRIS) on
the Keck I telescope at Mauna Kea Observatories in Hawaii. Both FORS and
LRIS are very efficient spectrographs, which allows the team to take spectra
of many stars in a galaxy simultaneously (in a single exposure). These stars
can then be studied individually later, when the data are analyzed to
determine atmospheric temperatures and surface gravities.
The talk at the AAS meeting will describe their analysis method. It will
also discuss the determination of the chemical composition of the individual
stars in distant galaxies and how the chemical composition changes from the
center of the galaxies to their outskirts.
Blue supergiant stars are the largest and brightest stars in the universe at
visual wavelengths, with an intrinsic brightness between 10,000 and 1000,000
times that of the sun. They appear blue in color because the temperature of
their atmospheres is 150 percent to 500 percent times than that of the sun.
Because of their blue color and their enormous brightness, they stand out
among the hundred billion stars in a galaxy, and so are easy to find and
identify. This makes them ideal for studying stellar populations in galaxies
beyond the Local Group (the group of galaxies that contains our own Milky
Way galaxy) to learn about distances, chemical composition, star formation
in galaxies, and the absorption of starlight by gas and dust between stars.
In the Milky Way, Deneb in the constellation Cygnus (the Swan) and Rigel in
Orion are two well-known blue supergiants.
The title of the paper being given at the AAS meeting is "Extragalactic
Stellar Astronomy -- Quantitative Spectroscopy of A Supergiants in Galaxies
beyond the Local Group."
The Institute for Astronomy at the University of Hawaii conducts research
into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff
are also involved in astronomy education, deep space missions, and in the
development and management of the observatories on Haleakala and Mauna Kea.
Established in 1907 and fully accredited by the Western Association of
Schools and Colleges, the University of Hawaii is the state's sole public
system of higher education. The UH System provides an array of
undergraduate, graduate, and professional degrees and community programs on
10 campuses and through educational, training, and research centers across
the state. UH enrolls more than 50,000 students from Hawaii, the U.S.
mainland, and around the world.
IMAGE CAPTION:
[http://www.ifa.hawaii.edu/info/press-releases/AAS/kud_ass07-630.jpg
(398KB)]
The spiral galaxy NGC 300. The green circles and squares indicate the blue
supergiant stars measured in this experiment. The objects within the circles
are 50 to 100 percent hotter than the sun, whereas the objects in the
squares have a temperature at least 300 percent that of the sun.
University of Hawai'i
Director's Office
2680 Woodlawn Drive, Honolulu, Hawaii 96822
(808) 956-8566 Fax: (808) 946-3467
Website: http://www.ifa.hawaii.edu
CONTACT:
Dr. Rolf-Peter Kudritzki (808) 956-8566 or Mrs. Karen Rehbock (808) 956-6829
FOR RELEASE: 2:30 p.m. Hawaiian Standard Time, May 28, 2007
ASTRONOMERS FIND NEW WAY TO MEASURE DISTANCE TO OTHER GALAXIES
Dr. Rolf-Peter Kudritzki of the Institute for Astronomy (IfA) at the
University of Hawaii at Manoa will report today on a new method used to
measure extragalactic distances accurately based on the stellar gravities
and effective temperatures of blue supergiant stars in galaxies beyond the
Local Group. The paper will be presented at the meeting of the American
Astronomical Society (AAS) in Honolulu. His collaborators for this project
are Drs. Fabio Bresolin and Miguel Urbaneja (IfA) and a group of astronomers
of the Universidad de Concepcion, Chile, led by Dr. Wolfgang Gieren.
Kudritzki and his collaborators observed the galaxy NGC 300, which is about
6 million light-years away and located in the constellation Sculptor, to
test this new method of measuring distances between galaxies. They took
spectra to measure the atmospheric temperature of the stars and their
surface gravity. With these measurements, they were able to determine the
intrinsic brightness of each star and then to compare the apparent
brightness with intrinsic brightness to find the distance.
They then compared their distance measurements to those made using Cepheid
variable stars, the traditional way to measure the distance to nearby
galaxies. "This new method works excitingly well," says Kudritzki. "It seems
that we can determine distances to other galaxies with an accuracy of five
percent, which opens a complementary way to constrain the Hubble constant
more precisely." The Hubble constant denotes the current rate of expansion
of the universe.
Their observations consisted of medium- and low-resolution spectra taken
with the Focal Reducer Spectrograph (FORS) on the European Southern
Observatory's Very Large Telescope in Paranal, Chile. Kudritzki was
instrumental in designing FORS while at the University of Munich before
coming to Hawaii in 2000. In its most recent work on other galaxies, the
project team has also used the Low Resolution Imaging Spectrometer (LRIS) on
the Keck I telescope at Mauna Kea Observatories in Hawaii. Both FORS and
LRIS are very efficient spectrographs, which allows the team to take spectra
of many stars in a galaxy simultaneously (in a single exposure). These stars
can then be studied individually later, when the data are analyzed to
determine atmospheric temperatures and surface gravities.
The talk at the AAS meeting will describe their analysis method. It will
also discuss the determination of the chemical composition of the individual
stars in distant galaxies and how the chemical composition changes from the
center of the galaxies to their outskirts.
Blue supergiant stars are the largest and brightest stars in the universe at
visual wavelengths, with an intrinsic brightness between 10,000 and 1000,000
times that of the sun. They appear blue in color because the temperature of
their atmospheres is 150 percent to 500 percent times than that of the sun.
Because of their blue color and their enormous brightness, they stand out
among the hundred billion stars in a galaxy, and so are easy to find and
identify. This makes them ideal for studying stellar populations in galaxies
beyond the Local Group (the group of galaxies that contains our own Milky
Way galaxy) to learn about distances, chemical composition, star formation
in galaxies, and the absorption of starlight by gas and dust between stars.
In the Milky Way, Deneb in the constellation Cygnus (the Swan) and Rigel in
Orion are two well-known blue supergiants.
The title of the paper being given at the AAS meeting is "Extragalactic
Stellar Astronomy -- Quantitative Spectroscopy of A Supergiants in Galaxies
beyond the Local Group."
The Institute for Astronomy at the University of Hawaii conducts research
into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff
are also involved in astronomy education, deep space missions, and in the
development and management of the observatories on Haleakala and Mauna Kea.
Established in 1907 and fully accredited by the Western Association of
Schools and Colleges, the University of Hawaii is the state's sole public
system of higher education. The UH System provides an array of
undergraduate, graduate, and professional degrees and community programs on
10 campuses and through educational, training, and research centers across
the state. UH enrolls more than 50,000 students from Hawaii, the U.S.
mainland, and around the world.
IMAGE CAPTION:
[http://www.ifa.hawaii.edu/info/press-releases/AAS/kud_ass07-630.jpg
(398KB)]
The spiral galaxy NGC 300. The green circles and squares indicate the blue
supergiant stars measured in this experiment. The objects within the circles
are 50 to 100 percent hotter than the sun, whereas the objects in the
squares have a temperature at least 300 percent that of the sun.