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           SKY & TELESCOPE'S NEWS BULLETIN - JULY 28, 2000
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NAKED-EYE ERUPTION OF DELTA SCORPII

The middle star in the row of three forming the head of Scorpius is undergoing a substantial outburst. It has brightened enough to change the look of this familiar constellation for skywatchers paying close attention. Normally magnitude 2.3, Delta Scorpii rose to magnitude 1.9 from June 30th to July 25th. The brightening may well continue.

Delta Scorpii (also named Dschubba, from the Arabic for "the Scorpionís Forehead") is a hot, highly luminous type B0 IV star about 500 light-years away in the Scorpius-Centaurus Association. The first person to notice a slight brightening was the dedicated variable-star observer Sebastian Otero of Argentina. Notified of the change, astronomers elsewhere took spectra of the star. They discovered that for the first time it was showing strong emission lines of hydrogen, turning it into a star of type Be.

Delta Scorpii may be following in the venerable footsteps of Gamma Cassiopeiae, a star of identical spectral type that forms the prototype of the Gamma Cas category of variables ó rapidly rotating Be stars evolving off the main sequence and undergoing episodes of equatorial mass loss. Gamma Cas brightened from about magnitude 2.25 to 1.6 in 1937 and remained near this peak for many months. It subsided to magnitude 3.0 by 1940, then took more than 15 years to brighten back to normal.

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Variable Star Network (VSNET)

July 25, 2000

*** News from VSNET ***

The most spectacular event of this week is the historical outburst of Delta Scorpii! Delta Scorpii is a bright naked-eye star, which forms the center of the three stars making the western border of the constellation. A catastrophe is occurring in this star!!

The first observer who noticed the change of this star was Sebastian Otero (Argentina), an intensive observer of the VSNET. Otero reported to VSNET that the star looks brighter than normal, and called for spectroscopic observation. Upon this notification, a group led by Spanish astronomer Fabregat confirmed the dramatic change in the star's spectrum. The object had no or little emission lines in the past, but the present observation confirmed the emergence of emission lines. The star was thus identified as a genuine Be (B-star with emission lines) star. Ths star is presently reported as magnitude 1.9 and looks like to brighten further, reported to have changed the impression of the constellation!

Such a striking outburst of a Be star is next the the spectacular event of gamma Cas in 1937 April, 63 years back! Please closely look at this naked-eye object (no telescope is necessary!) and report your observations to VSNET.

The key subscription lists are vsnet-be and vsnet-campaign-be. To subscribe, please send "vsnet-be and vsnet-campaign-be" to

vsnet-adm@kusastro.kyoto-u.ac.jp

Supernova 2000cx is another spectacular object. This object is confirmed to be a very luminous class of supernova type Ia. The object now reaches magnitude 13.5, and is a good target for deep-sky hunting!

Several interesting dwarf novae are reported in outburst, and await follow-up observations. TT Ind, 1H 1933+510 and V2051 Oph would be promising targets for CCD observers.

CCD observations of such targets are a relatively easy task for a 20-40cm telescope; simply take as many CCD frames (with exposure times 10-30 sec) as possible, spanning several hours per night. The only requirements are the weather and your patience! If you need more help on the observing technique, please feel free to ask on the vsnet-campaign list.

We would sincerely appreciate volunteers who would join the VSNET Collaboration team to study the wonders of these exotic variable stars. To join the VSNET campaign collaborative list, send an e-mail to

VSNET administrator

with a line "SUBSCRIBE vsnet-campaign."

(VSNET campaign members are strongly recommended to subscribe to vsnet-alert at the same time).

Jul. 24, 2000, as VSNET campaign circulation 389.

VSNET Weekly Campaign Summary

*** Last week news ***

(excerpt) Delta Sco (RA = 16h00m19s.9, Dec = -22d37'17")

S. Otero discovered that the bright B0.5IV star Delta Sco is probably brighter than the normal. He pointed out that, in the published photometric data, there is one isolate observation at 2.21mag in the normal 2.31 - 2.33mag. He suggested it is a possible gamma Cas (GCAS) variable (active Be stars). (vsnet-be 2). The spectroscopic confirmation that it is a new GCAS star, was reported in [vsnet-be 3] and IAUC 7461. Spectra taken with the 1.3m telescope at Skinakas Observatory (Crete, Greece) on July 19 revealed the H-alpha line in emission. The bright star delta Scorpii is currently undergoing a major optical and H-alpha outburst (vsnet-campaign-be 2). S. Otero reported the additional observations and estimated the rate of brightening to be +- 0.02 mag. per day (vsnet-campaign-be 4).

Delta Sco has now become one of the brightest GCAS stars among historically recorded outbursts of this class. Please watch closely and report your observations.


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