Delta Cancri
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cancer |
| Right ascension | 08h 44m 41.09921s[1] |
| Declination | +18° 09′ 15.5034″[1] |
| Apparent magnitude (V) | +3.94[2] |
| Characteristics | |
| Spectral type | K0 III[3] |
| U−B color index | +0.99[2] |
| B−V color index | +1.08[2] |
| Astrometry | |
| Radial velocity (Rv) | 16.39±0.25[4] km/s |
| Proper motion (μ) | RA: −17.67[1] mas/yr Dec.: −229.26[1] mas/yr |
| Parallax (π) | 24.98 ± 0.24 mas[1] |
| Distance | 131 ± 1 ly (40.0 ± 0.4 pc) |
| Absolute magnitude (MV) | +0.843[5] |
| Details | |
| Mass | 1.71[3] M☉ |
| Radius | 11[4] R☉ |
| Luminosity | 52[3] L☉ |
| Surface gravity (log g) | 2.7[4] cgs |
| Temperature | 4,637±27[3] K |
| Metallicity [Fe/H] | −0.13[4] dex |
| Rotational velocity (v sin i) | 2.8[4] km/s |
| Age | 2.45[3] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Delta Cancri (δ Cancri, abbreviated Delta Cnc, δ Cnc) is a double star about 180 light-years from the Sun in the constellation of Cancer.
Its two main constituents are designated Delta Cancri A and B. A is itself a binary star whose components are Delta Cancri Aa (formally named Asellus Australis /əˈsɛləs ɔːsˈtreɪlɪs/, the traditional name of the entire system)[6] and Ab.
The star system is 0.08 degree north of the ecliptic, so it can be occulted by the Moon and more rarely by planets; it is occulted (eclipsed) by the sun from about 31 July to 2 August.[7] Thus the star can be viewed the whole night, crossing the sky at the start of February.
Nomenclature
δ Cancri (Latinised to Delta Cancri) is the system's Bayer designation. The designations of the two constituents Delta Cancri A and B, and those of A's components - Delta Cancri Aa and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[8]
It bore the traditional name Asellus Australis which is Latin for "southern donkey colt".[9] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[10] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[11] It approved the name Asellus Australis for the component Delta Cancri Aa on 6 November 2016 and it is now so included in the List of IAU-approved Star Names.[6] Together with Gamma Cancri, it formed the Aselli, flanking Praesepe.[9]
As Arkū-sha-nangaru-sha-shūtu, which means "the southeast star in the Crab", it marked the 13th ecliptic station of the ancient Babylonians.[9]
In Chinese astronomy, Ghost (Chinese: 鬼宿; pinyin: Guǐ Xiù) refers to an asterism consisting of Theta Cancri, Eta Cancri, Gamma Cancri and Delta Cancri.[12] Delta Cancri itself is known as the fourth star of Ghost (Chinese: 鬼宿四; pinyin: Guǐ Xiù sì).[13]
Observations
Delta Cancri was involved in the first recorded occultation by Jupiter:
"The most ancient observation of Jupiter which we are acquainted with is that reported by Ptolemy in book X, chap. iii (sic), of the Almagest, ...when the planet eclipsed the star known as (Delta) Cancri. This observation was made on September 3, B.C. 240, about 18h on the meridian of Alexandria."
— Allen, 1898, quoting from Hind's The Solar System).
Delta Cancri also marks the famous open star cluster Praesepe (or the Beehive Cluster, also known as Messier 44). In ancient times M44 was used as a weather gauge as the following Greek rhyme from Aratos' Prognostica reveals:
A murky manger with both stars
Shining unaltered is a sign of rain.
While if the northern Ass is dimmed
By vaporous shroud, he of the south gleam radiant,
Expect a south wind: the vaporous shroud and radiance
Exchanging stars harbinger Boreas.
— Allen, 1898
The meaning of this verse is that if Asellus Borealis or Gamma Cancris[14] is hidden by clouds, the wind will be from the south and that situation will be reversed if Asellus Australis is obscured. There is some doubt however as to the accuracy of this as Allen notes: "Our modern Weather Bureau would probably tell us that if one of these stars were thus concealed, the other also would be." (Allen, 1898)
But Delta Cancri also acts as more than just a dubious weather guide: it is a reliable signpost for finding the vividly red star X Cancri as Patrick Moore notes in his guidebook Stars of the Southern Skies:
“In the same binocular field with Delta [Cancri] you will find one of the reddest stars in the sky: X Cancri. It is a semi-regular variable; at maximum it rises to magnitude 5 and it never falls below 7.3 so that it can always be seen with binoculars. It looks rather like a tiny glowing coal.”
— Page 146, Moore, 1994.
Delta Cancri also marks the radiant of the Delta Cancrids meteor shower.
In 1876, the possibility of Delta Cancri having a companion star was proposed.[15]
References
- ^ a b c d e van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
- ^ a b c Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
- ^ a b c d e Luck, R. Earle (September 2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 23, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114, 88.
- ^ a b c d e Massarotti, Alessandro; et al. (January 2008), "Rotational and radial velocities for a sample of 761 HIPPARCOS giants and the role of binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
- ^ Soubiran, C.; et al. (March 2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics, 480 (1): 91–101, arXiv:0712.1370, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788, S2CID 16602121.
- ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
- ^ In the Sky Earth astronomy reference utility showing the ecliptic and relevant date as at J2000 - present
- ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
- ^ a b c Allen, Richard Hinckley, Star Names: Their Lore and Meaning, 1898.
- ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
- ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
- ^ 陳久金 (2005). Zhōngguó Xīngzuò Shénhuà 中國星座神話 [Chinese Constellation Mythology]. 台灣古籍出版有限公司. p. 394. ISBN 978-986-7332-25-7.
- ^ 亮星中英對照表 [English-Chinese Glossary of Bright Stars]. Hong Kong Space Museum (in Chinese). Retrieved February 3, 2018.
Asellus Australis
- ^ Kaler, 2009:"ASELLUS BOREALIS". Archived from the original on 2011-07-16.
- ^ Burnham, S. W. (1878). "The companion to delta Cancri". The Observatory. 2: 60. Bibcode:1878Obs.....2...60B.
Books
- Richard H. Allen (28 February 2013). Star Names: Their Lore and Meaning. Courier Corporation. ISBN 978-0-486-13766-7.
- Robert Burnham (15 April 2013). Burnham's Celestial Handbook, Volume One: An Observer's Guide to the Universe Beyond the Solar System. Courier Corporation. pp. 340–. ISBN 978-0-486-31902-5.
- James B. Kaler (20 November 2006). The Cambridge Encyclopedia of Stars. Cambridge University Press. ISBN 978-0-521-81803-2.
- Lloyd Motz; Carol Nathanson (1 November 1988). The constellations. Doubleday.
- Patrick Moore (13 October 1998). Atlas of the Universe. Cambridge University Press. ISBN 978-0-521-64210-1.
- Patrick Moore (1994). Stars of the Southern Skies. Penguin. ISBN 978-0-14-024315-4.
