[AZ-Observing] Re: [amastro] theta-1 Ori E is an eclipser

From: "Wayne (aka Mr. Galaxy)" <mrgalaxy@xxxxxxxx>
To: amastro@xxxxxxxxxxxxxxx, az-observing@xxxxxxxxxxxxx, taaaforum@xxxxxxxxxxxxxxx
Date: Sat, 30 Jun 2012 01:02:47 GMT
15480 Empire Rd.
Benson, AZ 85602
hm ph: 520-586-2244 I wonder if the variation of star E in the Trapezium is 
more prominent in the visual part of the spectrum, Brian? I don't know how the 
infrared magnitude variations compare with the visual variations. I have had 
difficulty seeing star E at times and other times it has been as obvious as 
star F, which has always been fairly easy. I sent a query to Mati Morel a few 
months ago and mistakenly said I thought star F was variable (actually meaning 
star E) and wondering if he knew for a fact about its variability, but never 
heard back. I also read in an astro-ph (I think) notice about the time that 
Sabastian Otero from South America was making a map of the Trapezium. He was 
wondering whether star A, with its components the pair A1&A3 (= the variable 
star V1016 Ori with a period of 65.4 days) and star A2 with a separation of 
0.2arcsec, might be resolvable at their Mendocino Star Party. I thought the 
idea was preposterous, but lately I have been able to resolve (well, notch 
anyway) stars that are around 0.3+ arcsec with my 13-inch Dobsonian on a couple 
nights of very good seeing from my backyard and now think that Sebastian's 
suggestion might have some merit. I never heard back from anybody at the 
Mendocino Star Party whether they tried to resolve star A. It should be 
possible at the Winter Star Party in Florida, too, if the seeing is as good as 
people claim. I'll bet it should also be possible to do on Mt Wilson in 
California. When I worked on the proto-type of the adaptive optics system for 
the 60-inch telescope lo these many years ago I experienced some nights of 
excellent seeing there and claim to have resolved the disk of Vesta during one 
of my observations. The asteroid certainly appeared _larger_ than a star of 
comparable brightness in the same field of view, but I wonder if the effect may 
be caused by reflected light vs. emanated light. There was certainly a 
difference in the "luster" (as William Herschel would put it) between the two 
objects. It's similar to observing the disks of the Galilean moons around 
Jupiter.  Anyway, another, maybe easier, challenge might be star B of the 
theta-1 Ori (Trapezium) group. It forms a small group, whose four brightest 
members are the pairs B1&B5 and B2&B3 (the latter pair = the variable star BM 
Ori with a period of about 6.47 days) that should be bright enough and far 
enough to split. The B1 pair is about magn 8 and the B2 pair is about magn 10 
at its brightest. The separation of the two pairs is about 0.9arcsec. Worth a 
try when Orion becomes available again. I have been seeing the Pleiades already 
with Jupiter and Venus nearby in the morning sky! 
Clear skies, 
Wayne (aka Mr. Galaxy)
---------- Original Message ----------
From: Brian Skiff <bas@xxxxxxxxxx>
To: amastro@xxxxxxxxxxxxxxx
Subject: [amastro] theta-1 Ori E is an eclipser
Date: Wed, 27 Jun 2012 19:19:08 -0700


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 
"http://www.w3.org/TR/html4/strict.dtd";> 
While browsing the astro-ph preprint server this evening,
a paper by a large cabal centered at CalTech reports six new
pre-main-sequence eclipsing binary stars in the Orion Nebula region.
One of these is theta-01 Ori E, the "fifth" star in the Orion
trapezium. This star has long been thought to be variable, probably
for observational rather than astrophysical reasons. It has been
known to be a close binary for some time, with suspicion that it 
ought to be eclipsing.
Data taken with the Spitzer space telescope now show that the
two stars do indeed eclipse with period of 9.9 days and variation
(in the mid-infrared) of only 0.08 mag --- nothing that you would
see readily visually.
The lightcurve and existing radial velocities constrain the
types of stars involved. Visually the star appeared brick-red to me
when I viewed it one night many years ago using the Lowell 1.8-m
telescope. The spectral types are early-G, and the masses are about
2.8 solar masses each. I don't know how much mass-loss there would be 
as the stars come onto the main-sequence, but if it is not too much,
then they will end up as A-type stars, something like Vega or Sirius
something like 10 million years from now.
Details are here:

http://arxiv.org/abs/1206.6350

YSOVAR: Six pre-main-sequence eclipsing binaries
in the Orion Nebula Cluster

Morales-Calderón et al (accepted for the ApJ)

\\Brian


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[AZ-Observing] Re: [amastro] theta-1 Ori E is an eclipser

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