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HK Lacertae, HD209813, HIP109002

HK Lacertae is a orange to red eclipsing binary system giant star that can be located in the constellation of Lacerta. HK Lacertae is the brightest star in Lacerta based on the Hipparcos 2007 apparent magnitude. The star can not be seen by the naked eye, you need a telescope to see it.

HIP109002 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD209813.

HK Lacertae has alternative name(s), HK Lac.

Location of HK Lacertae

The location of the star in the galaxy is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For HK Lacertae, the location is 22h 04m 56.56 and +47d14`04.2 .

Proper Motion of HK Lacertae

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving 30.61 ± 0.32 miliarcseconds/year towards the north and 59.46 ± 0.44 miliarcseconds/year east if we saw them in the horizon.

HK Lacertae Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 96.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of HK Lacertae

HK Lacertae has a spectral type of K0III SB. This means the star is a orange to red giant star. The star is 7418.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24194.7968579200000000s. The star has a B-V Colour Index of 1.05 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,755 Kelvin.

HK Lacertae Radius has been calculated as being 8.60 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 5,985,173.91.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 9.26. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

HK Lacertae Apparent and Absolute Magnitudes

HK Lacertae has an apparent magnitude of 6.92 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of 1.02 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.86. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Distance to HK Lacertae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 6.62 which gave the calculated distance to HK Lacertae as 492.69 light years away from Earth or 151.06 parsecs. It would take a spaceship travelling at the speed of light, 492.69 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

In 2007, Hipparcos data was revised with a new parallax of 6.14 which put HK Lacertae at a distance of 531.21 light years or 162.87 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.

The star's Galacto-Centric Distance is 7,418.00 Parsecs or 24,194.80 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of HK Lacertae

The star is a eclipsing binary system RS Canum Venaticorum variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. HK Lacertae brightness ranges from a magnitude of 7.242 to a magnitude of 7.024 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 24.4 days (variability).

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

HK Lacertae Facts

Alternative Names

Traditional/Proper NameHK Lacertae
Short NameHK Lac
Hipparcos Library I.D.109002
Bonner DurchmusterungBD+46 3572
Henry Draper Designation209813

Visual Facts

Star Typegiant star
Absolute Magnitude1.02 / 0.86
Visual / Apparent Magnitude6.92
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)22h 04m 56.56
Declination (Dec.)+47d14`04.2
Galactic Latitude-6.72 degrees
Galactic Longitude95.92 degrees
1997 Distance from Earth6.62 Parallax (milliarcseconds)
 492.69 Light Years
 151.06 Parsecs
2007 Revised Distance from Earth6.14 Parallax (milliarcseconds)
 531.21 Light Years
 162.87 Parsecs
Galacto-Centric Distance24,194.80 Light Years / 7,418.00 Parsecs
Proper Motion Dec.30.61 ± 0.32 milliarcseconds/year
Proper Motion RA.59.46 ± 0.44 milliarcseconds/year
B-V Index1.05
Radial Velocity-23.60 ± 0.21 km/s
Spectral TypeK0III SB
Colour(K) Orange to Red

Variable Star Details

Variable Star ClassEclipsing binary system
Variable Star TypeRS Canum Venaticorum
Mean Variability Period in Days24.410
Variable Magnitude Range (Brighter - Dimmer)7.024 - 7.242

Estimated Facts

Luminosity (x the Sun)96.0000000
Calculated Effective Temperature4,755 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars


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