BY Draconis

Starbox begin
name=BY Draconis AB Starbox observe
epoch=J2000
ra=RA|18|33|55.7728cite web
url=http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=BY+Dra
title=SIBMAD query result: V* BY Dra -- Variable of BY Dra type
publisher=Centre de Données astronomiques de Strasbourg
accessdate=2008-04-18]
dec=DEC|+51|43|08.905
appmag_v=8.07
constell=Draco Starbox character
class=K6Ve
b-v=+1.19cite journal
last=Epps | first=E. A.
title=UBV photoelectric observations. I. Stars within 25 parasecs of the Sun. II. Stars in quasar, galaxy fields. III. Stars in Kapteyn selected areas. IV. Miscellaneous stars.
journal=Royal Observatory Bulletin
year=1972 | volume=176 | pages=77-115
url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1972RGOB..176..127E
accessdate=2008-04-18 ]
u-b=+0.99
variable=BY Dra Starbox astrometry
radial_v=−27±5
prop_mo_ra=186.62
prop_mo_dec=−324.90
parallax=60.90
p_error=0.73
parallax_footnote= Starbox visbin
reference=
name=BY Dra B
period=0.01637
axis=4.40±0.05
eccentricity=0.298±0.003
inclination=151.8±3.5 Starbox catalog
names=BY Dra, GJ 719, BD+51 2402, HD 234677, LTT 15477, SAO 31048, HIP 91009.

BY Draconis is a multi-star system in the constellation Draco. It consists of at least three components. Components A and B form a close binary star system with a short orbital period of only 5.98 days. These may be pre-main sequence objects that are still in the process of collapsing. Their individual spectroscopic classifications are dK5e and dK7e. They form the prototype of a class of variable stars known as BY Draconis variables.cite journal
last=Boden | first= A. F. | coauthors=Lane, B. F.
title=A Preliminary Visual Orbit of BY Draconis
journal=The Astrophysical Journal
year=2001 | volume=547 | issue=2 | pages=1071-1076
url=http://aps.arxiv.org/abs/astro-ph/0001138
accessdate=2007-02-04 ]

The third component (C) is, by comparison, widely separated from the A-B pair by an angular distance of 17 arcseconds, which corresponds to 260 AU at the estimated distance of this star system—where an AU is the average distance from the Earth to the Sun. Component C is an M5 class red dwarf star. There may be a fourth component to the system, orbiting with a 114 day period, but this has not been visually confirmed.

The variability of BY Draconis is caused by activity in the stellar photosphere called starspots, which are comparable to sunspots on the Sun, in combination with rapid rotation that changes the viewing angle of the activity relative to the observer. This variation has an average periodicity of 3.8285 days, but the brightness also changes over the course of several years—depending on the level of surface activity. Most observers believe that the primary star (A) is responsible for the variability as the secondary produces only a third of the total luminosity from the system. However, the spots may occur on both stars. Unlike the Sun, these spots may occur in the polar regions of the stars.cite journal
last=Pettersen | first=B. R.
coauthors=Olah, K.; Sandmann, W. H.
title=Longterm behaviour of starspots. II - A decade of new starspot photometry of BY Draconis and EV Lacertae
journal=Astronomy and Astrophysics Supplement Series
year=1992 | volume=96 | issue=3 | pages=497–504
url=http://adsabs.harvard.edu/abs/1992A%26AS...96..497P
accessdate=2008-04-18 ]

References

External links

* cite web
url=http://www.daviddarling.info/encyclopedia/B/BY_Draconis_star.html
title=BY Draconis star
publisher=The Internet Encyclopedia of Science
accessdate=2008-04-18