Asellus Primus (θ Boötis)

Asellus Primus, designated as Theta Boötis or 23 Boötis, is a main-sequence star located in the constellation of Boötes.

Key Facts & Summary

  • Asellus Primus is located at around 47.39 light-years / 14.53 parsecs away from the Solar System.
  • Asellus Primus is a main-sequence star of spectral type F7 V.
  • It has an apparent magnitude of 4.05, and an absolute magnitude of 3.25.
  • This star is around 4.131 times brighter than our Sun.
  • Asellus Primus has around 1.3 solar masses, and 1.733 solar radii, thus it is around three times bigger than our Sun.
  • The surface gravity on this star has been recorded at around 4.12 cgs.
  • Asellus Primus is hotter than our Sun, having surface average temperatures of around 6,265 K.
  • The rotational velocity of Asellus Primus is 29.2 km / 18.1 mi per second, while its radial velocity is at -11.60 km / -7.2 mi per second.
  • This star’s age is currently unknown.
  • Asellus Primus is overall the seventh brightest star in the constellation of Boötes, the celestial herdsman.
  • There are many interesting stars and deep-sky objects in the constellation of Boötes, such as  Arcturus, the fourth-brightest star in the night sky, Muphrid, a binary star system, Nekkar, a yellow giant star, Seginus, a Delta Scuti variable star, Alkalurops, a triple star system, Izar, another triple star system, Rho Boötis, an orange giant star, the globular cluster NGC 5466, the bright galaxies NGC 5248 and NGC 5676, the Seyfert galaxy NGC 5653, the Boötes Void, or the Hercules-Corona-Borealis Great Wall – the largest structure in the universe.
  • The constellation of Boötes is a part of the celestial sphere facing away from the plane of our Milky Way galaxy, and as such, it has few to almost zero globular clusters or nebulae. However, the constellation is prominent in many faint galaxies.
  • The best time to observe Asellus Primus and the other stars and deep-sky objects in Boötes is during the month of June when the constellation is the most prominent.

θ Boötis

Theta Boötis, also known as 23 Boötis, has the traditional name Asellus Primus, which comes from Latin, and translates to the “first donkey colt”.

Asellus Primus is one of the northernmost stars of the constellation of Boötes, and its traditional name was approved by the IAU in late 2016.

Formation

Asellus Primus formed from an interstellar medium of gas and dust. Gravity pulled the swirling gas and dust together and resulted in the seventh brightest star of Boötes, Theta Boötis.

The exact age of this star is unknown, however, there is an optical companion star, a class M dwarf, which is located at around 70 arcseconds away from Theta Boötis, that has the same motion through space, which implies that the two stars must also have a common origin.

Distance, Size, and Mass

Asellus Primus is located at around 47.39 light-years / 14.53 parsecs away from our Solar System. It can be seen with binoculars.

Asellus Primus has around 1.3 solar masses, or 130% of our Sun’s mass, and 1.733 solar radii, or 173.3% of our Sun’s radius, which means that it is more than three times bigger than our Sun.

Other Characteristics

Asellus Primus is a main-sequence star of spectral type F7 V. It has an apparent magnitude of 4.05 and an absolute magnitude of 3.25. It is around 4.131 times brighter than our Sun.

Asellus Primus has a surface gravity of at around 4.12 cgs. This star is hotter than our Sun, having surface average temperatures of around 6,265 K, thus it is 1.08 times, or 8% hotter than our Sun.

Изображение сохранено с внедрением настроек

The rotational velocity of Asellus Primus is 29.2 km / 18.1 mi per second, while its radial velocity is at -11.60 km / -7.2 mi per second. This star’s age is currently unknown.

Star System

Asellus Primus / Theta Boötis appears to be a single star, however, it has an 11th magnitude optical companion located at around 70 arcseconds.

This companion is a class M2.5 dwarf star that is separated by a minimum of 1,000 AUs ( 1 AU is the distance equivalent from the Earth to the Sun).

It is uncertain if the two stars are gravitationally bound, however, they do share a common motion through space, and thus, chances are high that both of them were born out of the same interstellar medium.

Location

Asellus Primus / Theta Boötis is located in the constellation of Boötes, the celestial herdsman. It is the seventh brightest star in this constellation.

Asellus Primus, along with Iota Boötis, Kappa Boötis, and Lambda Boötis, is located in the far north of the Boötes constellation. They are collectively known as the Aulad al Dhi’bah – “the whelps of the hyenas”.

The constellation of Boötes is one of the first 48 Greek constellations, listed by the legendary astronomer Ptolemy, in his 2nd century Almagest.

Boötes is now among the 88 modern constellations, being the 13th largest in the sky, stretching for around 907 square degrees. There are many interesting stars and deep-sky objects in the constellation of Boötes, such as  Arcturus, the fourth-brightest star in the night sky, Muphrid, a binary star system, Nekkar, a yellow giant star, Seginus, a Delta Scuti variable star, Alkalurops, a triple star system, Izar, another triple star system, Rho Boötis, an orange giant star, the globular cluster NGC 5466, the bright galaxies NGC 5248 and NGC 5676, the Seyfert galaxy NGC 5653, the Boötes Void, or the Hercules-Corona-Borealis Great Wall – the largest structure in the universe.

The constellation of Boötes is a part of the celestial sphere facing away from the plane of our Milky Way galaxy, and as such, it has few to almost zero globular clusters or nebulae. However, the constellation is prominent in many faint galaxies.

The best time to observe Asellus Primus and the other stars and deep-sky objects in Boötes is during the month of June when the constellation is the most prominent.

The Future

Asellus Primus will continue to exist for many millions of years. Until its age is estimated, its future is hard to predict. Since it is just 30% more massive than our Sun, this star can’t explode as a supernova.

Did you know?

  • Asellus Primus was from 4300 BC to 3942 BC, the closest star to the celestial north pole. Though it was visible to the naked eye, it remained too dim to be regarded as a pole star.
  • The Chinese know Asellus Primus as Tian Quang san – the Third Star of Celestial Spear.
  • The Celestial Spear – known as Tian Quang – is a Chinese asterism formed by Asellus Primus, Kappa Boötis, and Iota Boötis. It is part of the Purple Forbidden enclosure, being among the three enclosures.

Sources:

  1. Wikipedia
  2. Universeguide
  3. Theskylive

Image sources:

  1. https://theskylive.com/sky/stars/star-images/54/5404_800.jpg
  2. https://theskylive.com/sky/stars/finder-charts/theta-bootis-finder-chart.png?c=1586785670
  3. https://www.star-facts.com/wp-content/uploads/2019/09/Izar-1024×620.jpg?189db0&189db0
  4. https://bestdoubles.files.wordpress.com/2011/07/bootes1.jpg
  5. https://lh3.googleusercontent.com/proxy/ITvYreaQ0rV4cSrZeB3iRYyfl5HTbE0ishbvocK7_GPcTB5GgMf8yioKbj4D-DlbfMp7oze8GVb0XmrhtZ8YlCVeEqp0vP5OE48
  6. https://www.peoplesguidetothecosmos.com/constellations/arp302-hubble-sm.jpg