Press Release

Early Gemini North Results Feature Super Star Clusters, Details of Circumstellar Disks

By SpaceRef Editor
June 5, 2001
Filed under ,

From massive young star clusters swaddled in a dust cocoon 600 trillion
miles wide to intriguing structural details in a circumstellar disk
around a nearby binary star system, the 8-meter Gemini North telescope
is providing astronomers with some of their best-ever infrared views of
the processes of star and planet formation.

Other results released today from the first few months of routine science
operations at Gemini North on Mauna Kea include: early analysis of the
stellar population at the very dense center of the Milky Way that finds
recent starbirth activity and many faint, low-mass stars; similar
observations of individual stars at the center of the galaxy M33 that
show a surprising mix of old and new stars; and several insights into
quasars, including circumnuclear “disks” or “bars” on the scale of
thousands of parsecs across their host galaxies, which may be part of
their fuel supply, and tantalizing hints of the structure of the host
galaxies behind these enormously bright radio energy fountains.

“Gemini North is the first and only large telescope able to do mid-
infrared imaging of faint structures and the distribution of gas and
dust within them,” says Catherine Pilachowski, Deputy U.S. Gemini
Project Scientist at the National Optical Astronomy Observatory (NOAO)
in Tucson, AZ. “The large apertures of the two Gemini telescopes will
also allow them to look at very small or very distant structures in the
near-infrared, such as disks around young stars and the structure of
galaxies around distant quasars.”

Globular star clusters are among the most ancient objects in the Universe,
forming about the same time as the first galaxies. “While their formation
remains somewhat of a mystery, they clearly require conditions that are
uncommon in the Universe today,” says Kelsey Johnson, a doctoral student
at the University of Colorado in Boulder.

Based on their early Gemini data, Johnson and collaborators Bill Vacca
(Max Planck Institute, Garching, Germany) and Peter Conti (University
of Colorado) estimate that three baby globular star clusters deep in
the heart of the starburst galaxy Henize 2-10 are less than a million
years old, analogous to the first day of life for a human.

Packed into a relatively small area of space, each “super star cluster”
is believed to evolve over billions of years into globular clusters
like those orbiting the Milky Way.

Henize 2-10, located 32 million light-years from Earth in the constellation
Pyxis, is known to radiate as much as 10 times more energy in the infrared
than in optical and UV wavelengths, Vacca says. This suggests that there
is not only a large amount of newly formed stars and star clusters present,
but also a vast amount of dust in these massive objects.

Johnson and her colleagues believe that the three super star clusters
must be the “engine” that emits between 60 percent to 100 percent of the
infrared energy radiated by the galaxy. “Given the vigorous star formation
throughout Henize 2-10 as seen in optical light, it is remarkable that
only a handful of these objects could be responsible for all the infrared
light we see,” she says.

The researchers estimate the temperature of the dust shells surrounding
the infant clusters at a minus 130 degrees Celsius (minus 200 degrees
Fahrenheit). This may sound cold, but compared to the rest of the
Universe — which is just above absolute zero due to slight heating by
the cosmic microwave background — the temperatures of the dust shells
surrounding the infant stars are “really quite balmy,” Johnson notes.

“If we can study objects like globular clusters as they are forming,
then we should be able to learn more about the conditions in the early
Universe,” says Johnson, who is studying the clusters with a combination
of Gemini North and radio data from the National Science Foundation’s
Very Large Array.

“No globular cluster this massive has formed in our Milky Way galaxy for
the past 10 billion years,” Pilachowski notes. “We could be seeing the
outcome of an epoch of major galaxy mergers in the very early Universe.
Other Gemini images of faint ‘fuzz’ around quasars shows us that these
galaxy interactions did occur in the distant past.”

Daniel Potter of the University of Hawaii Institute for Astronomy used
the Hokupa’a adaptive optics system and the QUIRC near-infrared imager
on Gemini North to take a remarkably sharp and deep image of the
quadruple star system GG Tauri, and the dust disk surrounding the main
binary pair, GG Tauri A-B, about 450 light-years from Earth . The Gemini
image confirms a gap in the disk hinted at in earlier Hubble Space
Telescope images, and shows significant structure directly opposite the
gap.

“We clearly see that the gap is real,” Potter says. “But such a gap is
difficult to explain, because such a thing should last only a few thousand
years.” One explanation is that it is a shadowing effect from material
further inward in the disk, but it could also be a transitory feature due
to gravitational interaction between the binary stars.

“The filaments that seem to connect the central binary pair and the ring
have been reproduced in general hydrodynamical simulations of circumbinary
rings,” Potter adds. “A complex gravitational interaction between the disk
and the stars may also explain the ‘wavy’ structure seen on the inner
boarder of the ring. This image reveals a complex side of star formation
and disk evolution.”

Three images discussed this news release are available on the Internet at:
http://www.noao.edu/outreach/press/pr01/pr0109.html

The International Gemini Observatory is a multi-national collaboration that
has built two nearly identical 8-meter telescopes open to the worldwide
community of astronomers. Both telescopes incorporate new technologies
that allow large, relatively thin mirrors to collect and focus both optical
and infrared radiation from space.

The telescopes are located at Mauna Kea, Hawaii, (Gemini North) and Cerro
PachÛn in central Chile (Gemini South), and hence provide full coverage of
both hemispheres of the sky. Gemini North recently began routine science
operations and Gemini South is scheduled to begin scientific operations
in August 2001.

The Gemini Observatory is managed by the Association of Universities for
Research in Astronomy, Inc. (AURA) under a cooperative agreement with the
National Science Foundation (NSF). The NSF also serves as the executive
agency for the international partnership.

The other Gemini partnership research agencies include: the UK Particle
Physics and Astronomy Research Council (PPARC), the Canadian National
Research Council (NRC), the Chilean ComisiÛn Nacional de InvestigaciÛn
Cientifica y TecnolÛgica (CONICYT), the Australian Research Council (ARC),
the Argentinean Consejo Nacional de Investigaciones CientÌficas y TÈcnicas
(CONICET) and the Brazilian Conselho Nacional de Pesquisas Cientificas e
TecnolÛgicas (CNPq).

For more information, see the Gemini website at:
http://www.us-gemini.noao.edu/media/

Speakers in the June 4 special session in Room C106 at the AAS meeting will
include:

* Jean-Rene Roy (International Gemini Observatory, Hilo, HI) — Overview of
Gemini Capabilities

* Darren DePoy (Ohio State University, Columbus) — Galactic Center
Demonstration Science

* Kevin Luhman (Harvard-Smithsonian Center for Astrophysics, Cambridge,
MA) — A Search for Newborn Planets

* Sun Kwok (University of Calgary, Alberta, Canada) — Carbon-Rich PNe with
OSCIR

* Andy Stephens (Ohio State University) — The Bulge of M33

* Stephanie Plante (Laval University, Quebec City, Quebec, Canada) — Young
Supercluster in SBS 0335-052

* Charlie Telesco (University of Florida, Gainesville) — Early OSCIR Results

Kelsey Johnson presents her results in a related Gemini poster session in the
Exhibit Hall.

Daniel Potter will be speaking at a parallel oral session on Protostellar
Disks in Room C104.

Later in the meeting, Daniel Devost of Cornell University presents mid-
infrared observations of the luminous interacting galaxy NGC 3690 on
Thursday, June 7, in Session 81, Room C105, 10:00 a.m. to 11:30 a.m.

Olivier Guyon of the University of Hawaii Institute for Astronomy presents
observations of quasar host galaxies on Thursday, June 7, in Session 88,
Room C107, 2:00 p.m. to 3:30 p.m.

NOAO is operated by the Association of Universities for Research in
Astronomy (AURA), Inc. under cooperative agreement with the National
Science Foundation.

IMAGE CAPTIONS:

[Image 1: http://www.noao.edu/outreach/press/pr01/potter.shtml]
This near-infrared (H-Band) image of the disk around the binary star pair
GG Tauri A-B was obtained by the University of Hawaii’s adaptive optics
system called Hokupa’a, mounted on the Gemini North 8-meter telescope on
Mauna Kea in Hawaii on the night of February 24, 2001. Hokupa’a is the
Hawaiian word for the North Star and literally means “steady star.”

GG Tauri is a quadruple system (and possibly a quintuple system, with the
fifth component being a possible brown dwarf). Pictured here is the
circumbinary disk around the primary and secondary components, which are
separated by 0.24 arc-sec. GG Tauri is associated with the Tauris star-
forming region, about 450 light-years from Earth. The material around the
binary is known to be in Keplarian rotation around the two stars. The
combined mass of the stars are approximately 1.2 solar masses, and the
mass of the circumbinary ring has been measured to be about 0.3 solar
masses, based on millimeter wavelength studies. This ring is optically
thick in the H-Band, so what is seen is largely a reflection off the
surface of the ring material.

The inner 0.25 arc-sec surrounding the stars has been electronically masked
because the bright stars saturated the detector in this region. A “gap”
is shown at a position angle of 270 degrees referenced to GG Tau A, the
southern binary component. This gap was noted as speculative in observations
previously taken by HST/NICMOS, as it overlapped the telescope diffraction
spikes.

The inner boundary of the ring is not as smooth as the outer ring contours.
These structures are consistent with hydrodynamic simulations that show
transient flows of material onto the central stars (Atrymowicz and Lubow,
1996).

Credit: Daniel Potter/University of Hawaii Adaptive Optics Group/Gemini
Observatory/National Science Foundation

[Image 2: http://www.noao.edu/outreach/press/pr01/johnson.shtml]
Three massive dust cocoons seen in Gemini North observations with the
University of Florida’s OSCIR mid-infrared imager show “super star clusters”
deep in the heart of the starburst galaxy Henize 2-10 that are less than a
million years old, analogous to the first day of life for a human.

These observations correspond to at least three of the embedded radio
sources (white contours) discovered in Henize 2-10 by Kobulnicky & Johnson
in 1999. Astronomers believe these embedded star clusters represent the
early stages of globular cluster formation.

The dust cocoons may provide a glimpse into conditions in the early Universe
when galaxies were forming and the ancient massive star clusters surrounding
our Milky Way galaxy were created.

Credit: Kelsey Johnson/University of Colorado/Gemini Observatory/National
Science Foundation

[Image 3: http://www.noao.edu/outreach/press/pr01/guyon.shtml]
This image of quasar PG1411+442 was obtained using the University of
Hawaii’s adaptive optics system called Hokupa’a, mounted on the Gemini
North 8-meter telescope on Mauna Kea in Hawaii.

The quasar is the bright, overexposed object in the center of the picture.
Two tidal arms can be seen extending upward and downward from the quasar,
suggesting strongly that the host galaxy of PG1411+442 is the product of a
relatively recent galactic merger. A faint elongated companion can be seen
at the end of the upward tidal tail, which may be debris from the galactic
interaction. A very small faint companion galaxy is visible to the lower
left — it is also likely a part of this interacting system

PG1411+442 belongs to a class of Quasi-Stellar Objects (QSOs), or quasars,
called Infrared-Loud QSOs, which are characterized by strong infrared
luminosity. It has been suspected that QSOs are the result of galaxy
interactions, where the merger would first be seen as an Ultraluminous
Infrared Galaxy (ULIG), and later as a QSO. Infrared-Loud QSOs would
then represent the transition period between those two classes. These
observations of PG1411+442 fit very well with this theory.

Credit: Olivier Guyon/University of Hawaii Adaptive Optics Group/Gemini
Observatory/National Science Foundation

[Image 4: http://www.noao.edu/outreach/press/pr01/guyon.shtml#color]
This image is a smoothed version of an image of quasar PG1411+442 obtained
using the University of Hawaii’s adaptive optics system called Hokupa’a,
mounted on the Gemini North 8-meter telescope on Mauna Kea in Hawaii, with
a color scale added to highlight underlying details.

The quasar is the bright, overexposed object in the center of the picture.
Two tidal arms can be seen extending upward and downward from the quasar,
suggesting strongly that the host galaxy of PG1411+442 is the product of a
relatively recent galactic merger. A faint elongated companion can be seen
at the end of the upward tidal tail, which may be debris from the galactic
interaction. A very small faint companion galaxy is visible to the lower
left — it is also likely a part of this interacting system

PG1411+442 belongs to a class of Quasi-Stellar Objects (QSOs), or quasars,
called Infrared-Loud QSOs, which are characterized by strong infrared
luminosity. It has been suspected that QSOs are the result of galaxy
interactions, where the merger would first be seen as an Ultraluminous
Infrared Galaxy, and later as a QSO. Infrared-Loud QSOs would then
represent the transition period between those two classes. These
observations of PG1411+442 fit very well with this theory.

Credit: Olivier Guyon/University of Hawaii Adaptive Optics Group/Gemini
Observatory/National Science Foundation

SpaceRef staff editor.