Return to Home Page
Dear colleagues,
Distance of MisV1181
Seiichi Yoshida, John Greaves
We estimated the rough distance to MisV1181 (V709 Cep), a possible
nova discovered by the MISAO Project from unfiltered CCD images taken
in 2001.
The absolute magnitude of a nova can be estimated as:
M = -7.92 - 0.81 * arctan ( ( 1.32 - log(t2) ) / 0.23 )
where t2 indicates the days the nova fades two mag (della Valle and
Livio 1995).
MisV1181 was 12.7 mag on Sept. 19, 2001, and 14.3 mag on Nov. 10,
2001. It faded 1.6 mag during 52 days, which suggests t2 = 65 days.
Then, the absolute magnitude of MisV1181 is derived as -7 mag.
The distance modulus, apparent minus absolute magnitudes, is given as:
m - M = 5 * log(D) - 5 + A
where m is the apparent magnitude, M is the absolute magnitude, D is
the distance in parsec, and A is the absorption.
Assuming the absorption is normal, the absorption A is roughly equal
to the distance in kiloparsec. For instance, A is 5 mag for distance
of 5 kpc.
Assuming the maximum magnitude of MisV1181 is 12.5 mag, and the
absolute magnitude is -7 mag, the left side value (m - M) is 19.5.
If it was 5 kpc distant, the right side value becomes 18.5. If it was
6 kpc distant, the right side value becomes 19.9. Therefore, the
distance to MisV1181 is derived between 5 and 6 kpc.
The object lies towards the Cepheus Spiral Arm. From the Cepheus OB1
and OB2 associations which lie in the Cepheus Spiral Arm, this Spiral
Arm is about 3.5 kpc distant.
The derived distance implies that MisV1181 is beyond the Cepheus
Spiral Arm.
If it was inside the Cepheus Spiral Arm, i.e. 3.5 kpc distant, the
right side value would be 16.2, so the absolute magnitude would be
about -3.5 or -4 mag. It is too faint for a common nova.
In conclusion, MisV1181 is about 5 or 6 kpc distant, just inside the
Galaxy disk outer edge in that direction. Although it lies towards the
Cepheus Spiral Arm, MisV1181 is not inside the arm.
The exact distance is highly sensitive to the number of assumptions that
have to be followed on these matters, especially as some of the
fundamental parameters are not necessarily well known.
Reference:
della Valle, M., Livio, M., 1995, ApJ, 452, 704
Best regards,
--
Seiichi Yoshida
comet@aerith.net
http://vsnet.aerith.net/
Return to the Daisaku
vsnet-adm@kusastro.kyoto-u.ac.jp
