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IW Persei, HD21912, HIP16591

IW Persei is a blue rotating star that can be located in the constellation of Perseus. IW Persei is the brightest star in Perseus based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

HIP16591 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD21912.

IW Persei has alternative name(s), IW Per.

Location of IW Persei

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 IW Persei, the location is 03h 33m 35.02 and +39d53`58.5 .

Proper Motion of IW Persei

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 -45.63 ± 0.24 miliarcseconds/year towards the north and 14.80 ± 0.46 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of IW Persei

IW Persei has a spectral type of A5m. This means the star is a blue star. The star is 7449.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24295.9074945600000000s. The star has a B-V Colour Index of 0.13 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 8,061 Kelvin.

IW Persei Radius has been calculated as being 1.82 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,266,453.86.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 1.86. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

IW Persei Apparent and Absolute Magnitudes

IW Persei has an apparent magnitude of 5.79 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 2.10 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.05. 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 IW Persei

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 18.29 which gave the calculated distance to IW Persei as 178.33 light years away from Earth or 54.67 parsecs. It would take a spaceship travelling at the speed of light, 178.33 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 17.84 which put IW Persei at a distance of 182.83 light years or 56.05 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 7,449.00 Parsecs or 24,295.91 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 IW Persei

The star is a rotating Rotating ellipsoidal 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. IW Persei brightness ranges from a magnitude of 5.866 to a magnitude of 5.815 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.9 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.

IW Persei Facts

Alternative Names

Traditional/Proper NameIW Persei
Short NameIW Per
Hipparcos Library I.D.16591
Bonner DurchmusterungBD+39 811
Henry Draper Designation21912

Visual Facts

Star Type star
Absolute Magnitude2.10 / 2.05
Visual / Apparent Magnitude5.79
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 33m 35.02
Declination (Dec.)+39d53`58.5
Galactic Latitude-13.09 degrees
Galactic Longitude153.72 degrees
1997 Distance from Earth18.29 Parallax (milliarcseconds)
 178.33 Light Years
 54.67 Parsecs
2007 Revised Distance from Earth17.84 Parallax (milliarcseconds)
 182.83 Light Years
 56.05 Parsecs
Galacto-Centric Distance24,295.91 Light Years / 7,449.00 Parsecs
Proper Motion Dec.-45.63 ± 0.24 milliarcseconds/year
Proper Motion RA.14.80 ± 0.46 milliarcseconds/year
B-V Index0.13
Radial Velocity11.44 ± 0.31 km/s
Spectral TypeA5m
Colour(A) blue

Variable Star Details

Variable Star ClassRotating
Variable Star TypeRotating ellipsoidal
Mean Variability Period in Days0.917
Variable Magnitude Range (Brighter - Dimmer)5.815 - 5.866

Estimated Facts

Calculated Effective Temperature8,061 Kelvin

Sources and Links

SIMBAD SourceLink

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