BD +26730 suspected back in 1981

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BD +26730 suspected back in 1981

Post by marasama on 8th November 2008, 2:22 pm

Boy, this is an old paper. It state that there is suspected companion to BD +26730
http://adsabs.harvard.edu/abs/1981ApJ...249..662

http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=BD+%2B26+730
AND
http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD%20283750b (probably a BD)

Turns out, they knew this back in 1981 or earlier.
Mass constrained at.
-- mass of companion, 0.0002Ms if viewed edge-on
-- mass of companion, ~0.05 if rotation of the primary is synchornous which is the case for nearly all BY Dra system

It also stated that EQ Vir is similar in the Hα emission variability. I wonder if that means that EQ Vir should be looked at more?

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Re: BD +26730 suspected back in 1981

Post by Darkness nova on 13th November 2008, 12:43 am

*deleted*


Last edited by Darkness nova on 18th November 2008, 4:09 pm; edited 1 time in total

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Re: BD +26730 suspected back in 1981

Post by Lazarus on 13th November 2008, 7:04 am

0.0002 solar masses is the mass function, not the companion mass. Mass function is defined as

f(m) = (m sin i)3 / (M + m)2

Where f(m) is the mass function, M is the primary mass and m is the secondary mass.

From the paper:
If the orbit is viewed edge-on, and if we assume the primary has a mass of ~0.8 M, then the unseen secondary must be substellar (~0.05 M). However, if the rotation of the primary is synchronous with the orbit (as is the case for nearly all BY Dra systems) then we expect a rotation velocity v (equator) ~25 km s-1. The fact we observe v sin i≲15 km s-1 implies i≲35
...
We note that if i=30, the implied secondary mass M2 is 0.1M...
So a stellar companion, not substellar. See also this table from Cuntz, Saar and Musielak (2000), where the true mass is given as 132 Jupiter masses (well into the stellar regime).
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Re: BD +26730 suspected back in 1981

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