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A Look at NGC 3370 in Detail

The center of NGC 3370 shows well delineated dust lanes and an uncommonly ill-defined nucleus. 65kB 55kB Two regions on the edge of the galaxy show bright blue clusters of young, massive stars as well as distant, red background galaxies shining through. 48kB An unusual concentration in the upper corner shows a complex region of tidal interaction between a bright galaxy and its companion. Superimposed are a foreground star in the Milky Way and a background galaxy. 45kB A Sombrero-galaxy-look-alike is seen edge on with a small warp in the middle right. 48kB In the lower middle right, a distant filament of merging blue galaxies can be seen.

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Credit: NASA and A. Riess (STScI)

To Catch a (Rising and) Falling Star!

Supernova in NGC 3370

SN 1994ae was discovered by S. Van Dyk and the Leuschner Observatory Supernova Search (IAU Circular 6105) using an automated 0.76-meter telescope. The discovery image was taken on Nov. 14, 1994. The supernova was located about 30".3 west and 6".1 north of the galaxy's nucleus. The image on the left is from the 1.2-meter telescope at the Fred Lawrence Whipple Observatory (courtesy R. Schild/CfA) and was obtained in good conditions a few weeks after maximum light. The supernova peaked at ~13th magnitude in the visual.

NASA and A. Riess (STScI)

Extensive monitoring of the light curve in 5 colors was obtained beginning 2 weeks before maximum and provides one of the most complete photometric records of a supernova light curve (Riess et al. 1999). The image on the right is from HST 9 years later, by which time the supernova can no longer be detected. Many interesting features of the host as well as other background galaxies are blurred beyond recognition by the atmosphere in the ground-based image. HST, which sits above the distorting atmosphere, captures great detail at exquisite resolution.

Cepheid Variables in NGC 3370

Supernovae, such as SN 1994ae, can be used to calibrate distance measurements in the universe, because other, fainter stars of known brightness can be observed in the same galaxy. These stellar "standard candles" are the Cepheid variable stars, which vary regularly in brightness with periods that are directly related to their intrinsic brightness, and thus allow the distance to the galaxy--and the supernova--to be determined directly. However, only the Hubble Space Telescope, equipped with its new Advanced Camera for Surveys, has the capability to resolve these individual Cepheids in NGC 3370.



Above we see a "movie" of 12 consecutive epochs of a long period (~50 days) Cepheid variable. The Cepheid is in the center of a crowded region of stars. The resolution of HST is required to pick out the variable star from its neighbors. The star was caught initially fading before suddenly doubling in brightness, then declining again to its faintest point over 4-5 weeks. By plotting the change in brightness (magnitude) over time (days) we can see how the cepheid intensity rises and falls. At right is a "light curve" of the brightness over time for one of the cepheid variables in NGC 3370. Peak-to-trough variation, or from its faintest to its brightest, represents a doubling in brightness.

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Credit: NASA and A. Riess (STScI)