ULTRAVIOLET IMAGE OF STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD
TABLE OF CONTENTS:
SPIRAL GALAXY MESSIER 101 PHOTOGRAPHED BY THE ULTRAVIOLET IMAGING TELESCOPE
Release Date: 12 June 1995
This ultraviolet image of the giant spiral galaxy Messier 101 (M101) was obtained by the Ultraviolet Imaging Telescope during the Astro-2 mission of the Space Shuttle Endeavour.
M101 is an Sc-type galaxy, meaning a spiral galaxy with a relatively small central bulge and a system of spiral arms that is not tightly wound. At a distance of about 16 million light years, it is considered relatively close to the Earth.
M101 is known to contain many giant HII regions, meaning huge glowing nebulae shine as a result of ultraviolet radiation from the massive stars within them. The UIT images will be used to determine the far-ultraviolet energy outputs of these stars and nebulae. Also, the astronomers will study the ages of the nebulae, their dust contents, and the "initial mass functions" of their stars, meaning the relative numbers of stars of different masses when they first formed in the nebulae. This is equivalent to finding the relative numbers of newborn babies of different weights. The investigators will also determine the total mass of all the young massive stars in each HII region or nebula.
UIT is a 15-inch (0.38-m) telescope which was designed and built at the Goddard Space Flight Center, Greenbelt, MD. This UIT photo was presented to the American Astronomical Society meeting in Pittsburgh, Pa., June 12, 1995.
Technical Data: The exposure time was 1310 seconds and the photograph was made at an effective wavelength of 1520 angstroms (152 nanometers), with a bandwidth of 354 angstroms (35.4 nanometers). The photograph was obtained during nighttime portion of Endeavour's orbit on March 11, 1995. The region shown here is about two-thirds the apparent diameter of the full moon. The original UIT image was recorded on black and white film; the image is displayed here with color coding indicating intensity of the ultraviolet light.
ULTRAVIOLET IMAGE OF STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD
Release Date: 12 June 1995
This arc of hot stars in the star-forming region N 51 in the Large Magellanic Cloud (LMC) was photographed by NASA's Ultraviolet Imaging Telescope (UIT) during the Astro-2 mission of Space Shuttle Endeavour, March 2-18, 1995. The LMC is about 160,000 light- years from the Earth, and appears in the constellation Dorado, which is visible from the Earth's southern hemisphere.
This region contains at least 5 clusters of young, massive stars which have lifetimes of only a few million years. UIT's ultraviolet images are particularly useful for studying these stars since they are so hot that most of their energy is radiated in ultraviolet light, which is blocked from the view of telescopes on the ground by the Earth's atmosphere. The UIT scientists will analyze these images to learn how such massive stars form and how they effect their environment. The N 51 region is also a strong source of x-rays, resulting from the prodigious winds of these hot stars and from supernovae explosions created when such stars end their lives. The well-defined shape of the arc may be the result of a wave of star formation propagating through the LMC galaxy. The length of the arc is about 1000 light-years.
UIT is a 15-inch (0.38-m) telescope which was designed and built at the Goddard Space Flight Center, Greenbelt, MD. This UIT photo was presented to the American Astronomical Society meeting in Pittsburgh, Pa., June 12, 1995.
Technical Data: The exposure time was 792 seconds and the photograph was made at an effective wavelength of 1620 angstroms (162 nanometers), with a bandwidth of 220 angstroms (22 nanometers). The photograph was obtained during the daytime portion of Endeavour's orbit on March 14, 1995. The region shown here is about one and one-third times the apparent diameter of the full moon; objects appearing to be 1,000 times smaller than this can be resolved in this image. The original UIT image was recorded on black and white film; the image is displayed here with color coding indicating intensity of the ultraviolet light.
SMALL MAGELLANIC
CLOUD: A MOSAIC OF FOUR ULTRAVIOLET IMAGES
Release date: 12 June 1995
This is a mosaic of four ultraviolet photographs of the Small Magellanic Cloud obtained on both the Astro-1 mission (December 1990) and the Astro-2 mission (March 1995).
The Small Magellanic Cloud (SMC) is an irregular galaxy and a near neighbor to our Milky Way Galaxy. The SMC is about 190,000 light-years from the Earth, and appears in the constellation Tucana, which is visible from the Earth's southern hemisphere. This picture is a mosaic of four separate images obtained during the Astro-1 and Astro-2 missions and is the first complete ultraviolet picture of the SMC. Three of the images were obtained during Astro-2, and one during Astro-1.
These data will allow astronomers to make a detailed census of the hottest and youngest massive stars in the SMC. These objects, called O-type stars, may range up to over 100 times the mass of our Sun and are much rarer than ordinary stars like our sun. The star cluster NGC 346 in the top of this picture, contains over 40 O-type stars as well as a Wolf-Rayet star. Wolf-Rayet stars are a evolved O stars, meaning such stars are in a more advanced stage of their lives, and have extremely strong stellar winds; in less than 50,000 years, the winds from a Wolf-Rayet star can strip more material off the star than the entire mass of our Sun. The UIT scientists will analyze these images to learn how such massive stars form and how they effect their environment.
UIT is a 15-inch (0.38-m) telescope which was designed and built at the Goddard Space Flight Center, Greenbelt MD. This UIT photo was presented to the American Astronomical Society meeting in Pittsburgh, PA, June 12, 1995.
Technical Data: This is a mosaic of 4 separate images. Three were taken during Astro-2 (March 2-15, 1995); the fourth was taken during Astro-1 (December 2-10, 1990). All four photographs were made with an effective wavelength of 1620 angstroms (162 nanometers), with a bandwidth of 220 angstroms (22 nanometers), with exposure times between 118 seconds and 899 seconds. The region shown here approximately 120 arcminutes (2 degrees) by 40 arcminutes, totaling about five times the apparent diameter of the full moon. The original UIT images were recorded on black and white film; the image is displayed here with color coding indicating intensity of the ultraviolet light.
UIT AND
GROUND-BASED IMAGING OF THE STARBURST GALAXY NGC4736 Release date: 12 June 1995
A remarkable giant ring of hot young stars appears in the ultraviolet image (top) of the spiral galaxy Messier 94 (M94, also called NGC 4736), as photographed by the Ultraviolet Imaging Telescope on March 12, 1995 during the Astro-2 mission of the Space Shuttle Endeavour.
M94, called a starburst galaxy because of the large number of new hot stars that are present, is located about 15 million light years from Earth and has an apparent diameter equal to about 1/3 that of the full moon.
In red light (bottom), M94 shows three distinct zones: an extremely bright central bulge, composed mostly of old, cool stars; the main disk showing many short spiral arms; and an extensive, faint outer ring.
In striking contrast to its visual appearance, the UIT image (top) shows a completely different structure. Gone is the familiar spiral pattern, replaced by a well-defined ring of massive stars bracketing the nucleus. The central bulge is not observed. The stars in this ring formed within the past 10 million years, marking the ring as a site of intense, recent (in astronomical terms) star formation. A mystery, which UIT astronomers will explore, is why almost all massive star formation in M94 is concentrated in a very narrow zone and has not occurred in other parts of the galaxy. Study of the young stars in this ring will add to astronomer's understanding of galaxy evolution.
UIT is a 15-inch (0.38-m) telescope which was designed and built at the Goddard Space Flight Center, Greenbelt, MD. This UIT photo was presented to the American Astronomical Society meeting in Pittsburgh, Pa., June 12, 1995.
Technical Data: The exposure time for the UIT image was 1040 seconds and the photograph was made at an effective wavelength of 1520 angstroms (152 nanometers), with a bandwidth of 354 angstroms (35.4 nanometers). The photograph was obtained during the nighttime portion of Endeavour's orbit on March 12, 1995. The region of the galaxy M94 shown here is about one-quarter of the apparent diameter of the full moon. The original UIT image was recorded on black and white film; the image is displayed here with color coding indicating intensity of the ultraviolet light.
BOTTOM - Image of the same galaxy in red light, made with a 36-inch (0.9 meter) telescope at Kitt Peak National Observatory, near Tuscon Arizona. The image is displayed here with color coding indicating intensity of the red light. Red light image courtesy of W. H. Waller (Tufts University)
ULTRAVIOLET IMAGE OF NGC6752 HIGLIGHTS EVOLVING STARS
Release date: 12 June 1995
The globular cluster NGC 6752, in the southern constellation of Pavo, as seen at in ultraviolet light a wavelength of 1620 Angstroms with the Ultraviolet Imaging Telescope (UIT). The photograph was obtained on March 13, 1995, during the Astro-2 mission of the Space Shuttle Endeavour.
Although NGC 6752 contains more than one hundred thousand stars, nearly all of these are too cool to emit any ultraviolet light. The 355 stars seen in the UIT image are in a short-lived stage near the end of their lives (known as the horizontal branch phase) when they can reach a surface temperature of up to 30,000 degrees. The UIT image is able to resolve the hot stars into the cluster core, while the UIT 40 arcminute field of view is big enough to encompass the entire cluster. Thus, the UIT image provides the first complete census of the hot horizontal branch stars in NGC6752.
The overexposed bright star about 4 arcminutes southwest of the cluster center is the foreground star HD 177999 (with a visual brightness of 7.5 magnitudes and spectral type of A0) and is unrelated to the globular cluster.
UIT is a 15-inch (0.38-m) telescope which was designed and built at the Goddard Space Flight Center, Greenbelt, MD. NASA's UIT instrument flew in space during the Astro-2 mission of Space Shuttle Endeavour, March 2-18, 1995. This UIT photo was presented to the American Astronomical Society meeting in Pittsburgh, Pa., June 12, 1995.
Technical Data: The exposure time was 781 seconds and the photograph was made at an effective wavelength of 1620 angstroms (162 nanometers), with a bandwidth of 220 angstroms (22 nanometers). The photograph was obtained during the daytime portion of Endeavour's orbit on March 13, 1995. The region shown here is about the apparent diameter of the full moon; objects appearing to be 1,000 times smaller than this can be resolved in this image. The original UIT image was recorded on black and white film; the image is displayed here with color coding indicating intensity of the ultraviolet light.
ASTRONOMERS GET ULTRAVIOLET LOOK AT THE MOON Release Date: 12 June 1995
A Photo of the full Moon at invisble ultraviolet (UV) wavelengths (only observable from space) on the left is compared with a visible photograph (from a ground-based observatory) on the right. The brightest UV areas probably correspond with regions where the most recent resurfacing has occurred---such as in the vicinity of the bright-rayed impact crater Tycho near the lunar south pole. This UV photograph was made with the Ultraviolet Imaging Telescope (built by Ted Stecher and colleagues at NASA's Goddard Space Flight Center in Greenbelt, Maryland), part of the Astro-2 payload flown aboard the Space Shuttle Endeavour in March, 1995. This material was presented to the American Astronomical Society meeting in Pittsburgh, Pennsylvania on June 12, 1995.
Photo Credits:
Ultraviolet image of the Moon: Southwest Research Institute
Visible image of the Moon: Lick Observatory image
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