Delta Hydri

δ Hydri
	Location of δ Hydri (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Hydrus
Right ascension	02h 21m 44.94286s
Declination	−68° 39′ 33.9038″
Apparent magnitude (V)	4.09
Characteristics
Spectral type	A2 V
U−B color index	+0.05
B−V color index	+0.03
Astrometry
Radial velocity (Rv)	+6.00 km/s
Proper motion (μ)	RA: -49.95 mas/yr ; Dec.: +2.48 mas/yr
Parallax (π)	23.35±0.34 mas
Distance	140 ± 2 ly ; (42.8 ± 0.6 pc)
Absolute magnitude (MV)	0.92
Details
Mass	2.25 M☉
Radius	2.3 R☉
Luminosity	39.52 L☉
Surface gravity (log g)	3.98 cgs
Temperature	9,880±336 K
Metallicity [Fe/H]	+0.12 dex
Rotational velocity (v sin i)	162 km/s
Age	209 Myr
Other designations
	δ Hyi, CPD−69°113, FK5 1065, GC 2872, HD 15008, HIP 11001, HR 705, SAO 248545
Database references
SIMBAD	data

Delta Hydri, Latinized from δ Hydri, is a single,^[7] white-hued star in the southern constellation of Hydrus. It is bright enough to be faintly visible to the naked eye with an apparent visual magnitude of 4.09.^[2] The distance to this star, based upon an annual parallax shift of 23.35 mas,^[1] is about 140 light years. It is moving away from the Sun with a radial velocity of +6 km/s.^[4]

This is an ordinary A-type main-sequence star with a stellar classification of A2 V^[3] It is about 209 million years old and has a high rate of spin, showing a projected rotational velocity of 162 km/s.^[6] This is giving the star an oblate shape with an equatorial bulge that is 7% larger than the polar radius.^[8] The star has 2.25 times the mass of the Sun and 2.3 times the Sun's radius.^[5] It is radiating 39.5^[3] times the Sun's luminosity from its photosphere at an effective temperature of around 9.880.^[6] Delta Hydri has been checked for an infrared excess, but none was found.^[7]

References

^ ^a ^b ^c ^d ^e ^f 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. Vizier catalog entry
^ ^a ^b ^c ^d Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
^ ^a ^b ^c ^d ^e ^f Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644. Vizier catalog entry
^ ^a ^b Kharchenko, N.V.; Scholz, R.-D.; Piskunov, A.E.; Röser, S.; Schilbach, E. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID 119323941.
^ ^a ^b ^c Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555–562. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. Vizier catalog entry
^ ^a ^b ^c ^d ^e ^f David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. S2CID 33401607. Vizier catalog entry
^ ^a ^b Rodriguez, David R.; et al. (May 2015), "Stellar multiplicity and debris discs: an unbiased sample", Monthly Notices of the Royal Astronomical Society, 449 (3): 3160–3170, arXiv:1503.01320, Bibcode:2015MNRAS.449.3160R, doi:10.1093/mnras/stv483, S2CID 119237891.
^ van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.

[vanLeeuwen2007-1] ^ ^a ^b ^c ^d ^e ^f 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. Vizier catalog entry

[Ducati2002-2] Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.

[XHIP-3] ^ ^a ^b ^c ^d ^e ^f Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644. Vizier catalog entry

[Kharchenko2007-4] Kharchenko, N.V.; Scholz, R.-D.; Piskunov, A.E.; Röser, S.; Schilbach, E. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID 119323941.

[AllendePrieto-5] Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555–562. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. Vizier catalog entry

[David2015-6] ^ ^a ^b ^c ^d ^e ^f David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. S2CID 33401607. Vizier catalog entry

[Rodriguez2015-7] Rodriguez, David R.; et al. (May 2015), "Stellar multiplicity and debris discs: an unbiased sample", Monthly Notices of the Royal Astronomical Society, 449 (3): 3160–3170, arXiv:1503.01320, Bibcode:2015MNRAS.449.3160R, doi:10.1093/mnras/stv483, S2CID 119237891.

[vanBelle2012-8] van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.

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Observation data Epoch J2000 Equinox J2000
Location of δ Hydri (circled)
Constellation	Hydrus
Right ascension	02^h 21^m 44.94286^s^[1]
Declination	−68° 39′ 33.9038″^[1]
Apparent magnitude (V)	4.09^[2]
Characteristics
Spectral type	A2 V^[3]
U−B color index	+0.05^[2]
B−V color index	+0.03^[2]
Astrometry

Radial velocity (R_v)	+6.00^[4] km/s
Proper motion (μ)	RA: -49.95^[1] mas/yr Dec.: +2.48^[1] mas/yr
Parallax (π)	23.35±0.34 mas^[1]
Distance	140 ± 2 ly (42.8 ± 0.6 pc)
Absolute magnitude (M_V)	0.92^[3]

Details

Mass	2.25^[5] `M`_☉
Radius	2.3^[5] `R`_☉
Luminosity	39.52^[3] `L`_☉
Surface gravity (log g)	3.98^[6] cgs
Temperature	9,880±336^[6] K
Metallicity [Fe/H]	+0.12^[3] dex
Rotational velocity (v sin i)	162^[6] km/s
Age	209^[6] Myr

Other designations
δ Hyi, CPD−69°113, FK5 1065, GC 2872, HD 15008, HIP 11001, HR 705, SAO 248545
Database references
SIMBAD	data

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