DELTA VELORUM 1.gif
Dear friends:
In spite of the complaints about
attachments (in vsnet) and whatever, I will be a bad boy and break the rules
one more time, because I think this situation deserves it. (They are only 14
KB...)
VERY IMPORTANT NEWS on a VERY BRIGHT STAR again !!!!!! And it's another
DELTA...
It has come to my attention, from a note
by Danie Overbeek (incidentally forwarded to me by Brian Fraser), that Paul
Fieseler of NASA has noted a dip in light output of delta Velorum in data
from the Galileo spacecraft's star scanner.
For Paul Fieseler's attention I can say
that the event was most probably real and not an instrumental feature, as of
I have been monitoring delta Velorum for several years visually and have
detected three eclipses in that time, as shown by the attached GIF of my
visual estimates.
I first noticed the fading on July 1997
when the star was observed at 2.2 instead of its normal 1.95. For 200 days
nothing happened and then again it dropped down to 2.2. Since 1997 I have
recorded three probable eclipses.
Searching through the Hipparcos Catalogue
Epoch Photometry Data I could find that one single transit observation (on
BJD 2448806) out of 112 transits shows a 2.21 Hp (V= 2.20) instead of the
classical 1.95. Too much of a coincidence.
Preliminary investigations of the data,
undertaken with John Greaves, had suggested a period of 67.7 days...: It is
interesting to note that my last recorded eclipse, centred about JD
241308.7, is exactly 6 times 67.7 days from JD 2451714.9, or 10am UT on June
19 2000, which I believe is the central time of the event observed by
Fieseler.
Another possibility is a 5.88854
day-period. The longer one joins three of the eclipses and the shorter joins
all. But it's strange that such a short period eclipser has remined unseen!!
Coincidentlly, I was just about to start an
intensive campaign soon so in this light it will be very urgent to get
started.(Although right now the star is in its worst position...)
As can be seen from the attached GIF (where
I included Galileo's disappearance), I have monitored this star regularly
and found no hint of frequent eclipse.
I had waited three years for the fourth
(five counting Hipparcos) event and it happened before Galileo's eyes
(Galileo was seeing well!) !!!!!!!
The time of mideclipse is then 2451714.9375 and it agrees exactly with both
the 67.7 and the 5.88854 day-periods.
So, the shorter period fits OK with most of the data but would mean a short
eclipse time, which seems to be not possible according to Galileo's
disappearance.
And the longer period joins three of the four eclipses, and gives an
approximation to the rest.
If 67.7 days, or submultiple thereof, is a valid and reasonably accurate
figure, then it should be noted that given the JD 2451714.9 mid-event timing
of the Galileo observations, and also the JD 2451308.7 mid-eclipse timing
from my last recorded visual event, the next eclipse should occur at:
JD 2451850.3 20001101.8
JD 2451918.0 20010108.5
JD 2451985.7 20010316.2
JD 2452053.4 20010522.9
The star should be monitored for a few days either side of the predicted
times.
If the period is 5.88854 days, then the corresponding eclipses would take
place at:
JD 2451850.4 20000101.9
JD 2451915.1 20010105.6
JD 2451921.0 20010111.5
JD 2451985.8 20010316.3
JD 2452050.6 20010520.1
JD 2452056.5 20010526.0
So the question is going to be settled soon
I was hoping to make one more eclipse observation to further refine this
aspect before making an announcement.
It is difficult to announce to the world that one of the apparent brightest
stars in the sky has been visually
detected as a previously unknown eclipsing binary of low amplitude without
being able to say when it will next happen!
It's interesting to note that this spectroscopic binary nature for the A
star (We could call it Ax for now) ends with a long time discrepancy between
the absolute magnitude prdicted by theory for delta Vel A (1.0 for an A1V
star) and the actually observed (0.4)
Probably they are both A stars and that made the detection harder.
A good picture could be (V apparent magnitudes, probable spectral types
suggested by the combined color index and the magnitudes of the components):
A= 2.8 , A0V
x= 3.3 , A3:V
P= 3.6 , A5:V:
B= 5.5 , A9:V:
Up to now it was known that P was 1.6 mag. fainter than A [Tango, Davis,
Thompson & Brown, proc. ASA, 1979] (actually Ax) and that the AP combined
magnitude was V=1.99.
But these kind of speculations will have to wait.
We've got work to do!!!!!
Thanks to John Greaves for his support and knowledge.
Best regards,
Sebasti睹 Otero,( LIADA - Liga Iberoamericana de Astronom)
Buenos Aires,
Argentina.
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