XO-4

Star in the constellation Lynx

XO-4 / Koit
Observation data Epoch J2000 Equinox J2000
Constellation	Lynx^[1]
Right ascension	07^h 21^m 33.1602^s^[2]
Declination	+58° 16′ 05.110″^[2]
Apparent magnitude (V)	10.674 ± 0.019^[3]
Characteristics
Spectral type	F5V^[3]
Apparent magnitude (B)	11.240 ± 0.029^[3]
Apparent magnitude (V)	10.674 ± 0.019^[3]
Apparent magnitude (J)	9.667 ± 0.021^[4]
Apparent magnitude (H)	9.476 ± 0.022^[4]
Apparent magnitude (K)	9.406 ± 0.023^[4]
Astrometry

Proper motion (μ)	RA: −17.008(12) mas/yr^[2] Dec.: 5.463(12) mas/yr^[2]
Parallax (π)	3.7812 ± 0.0156 mas^[2]
Distance	863 ± 4 ly (264 ± 1 pc)

Details

Mass	1.32 ± 0.02^[3] `M`_☉
Radius	1.56 ± 0.05^[3] `R`_☉
Temperature	6397 ± 70^[3] K
Metallicity [Fe/H]	-0.04 ± 0.03^[3] dex
Age	2.1 ± 0.6^[3] Gyr

Other designations
Koit, TYC 3793-1994-1, GSC 03793-01994, 2MASS J07213317+5816051^[5]
Database references
SIMBAD	data

XO-4 is a star located approximately 863 light-years away from Earth in the Lynx constellation. It has a magnitude of about 11 and cannot be seen with the naked eye but is visible through a small telescope.^[3] A search for a binary companion star using adaptive optics at MMT Observatory was negative.^[6]

The star XO-4 is named Koit. The name was selected in the NameExoWorlds campaign by Estonia, during the 100th anniversary of the IAU. Koit is Estonian for dawn, and was named for a character in a folk tale written by Friedrich Robert Faehlmann.^[7]^[8]^[9]

Planetary system

One known exoplanet, XO-4b, which is classified as a hot jupiter, orbits XO-4. This exoplanet was discovered in 2008 by the XO Telescope project using the transit method.^[3] It has been named Hämarik, meaning dusk, and referring to a character from the same Faehlmann story featuring Koit.^[10]

The XO-4 planetary system^[3]^[11]^[12]
Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b / Hämarik	1.72 ± 0.20 M_J	0.0552 ± 0.0003	4.1250823 ± 0.0000039	0(assumed) ^{[note 1]}	—	—

Notes

^ eccentricity approximately equal to zero is expected theoretically and is consistent with the radial velocities and secondary eclipses timing^[3]^[12]

References

^ Roman, Nancy G. (1987). "Identification of a Constellation From a Position". Publications of the Astronomical Society of the Pacific. 99 (617): 695–699. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Vizier query form
^ ^a ^b ^c ^d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m McCullough, P. R.; et al. (2008). "XO-4b: An Extrasolar Planet Transiting an F5V Star". arXiv:0805.2921 [astro-ph].
^ ^a ^b ^c Cutri; et al. (2003). "2MASS===07213317+5816051". 2MASS All-Sky Catalog of Point Sources. Retrieved 2012-02-25.
^ "SIMBAD query result: TYC 3793-1994-1 -- Star". Centre de Données astronomiques de Strasbourg. Retrieved 2009-04-26.
^ Adams, E. R.; et al. (2013). "Adaptive Optics Images. II. 12 Kepler Objects of Interest and 15 Confirmed Transiting Planets". The Astronomical Journal. 146 (1). 9. arXiv:1305.6548. Bibcode:2013AJ....146....9A. doi:10.1088/0004-6256/146/1/9. S2CID 119117620.
^ "Approved names". NameExoworlds. Retrieved 2020-01-02.
^ "International Astronomical Union | IAU". www.iau.org. Retrieved 2020-01-02.
^ "Estonia has been assigned its own star and planet". Estonian World. 20 January 2020. Retrieved 2020-01-20.
^ "Estonia has been assigned its own star and planet". Estonian World. 20 January 2020. Retrieved 2020-01-20.
^ Narita, Norio; et al. (2010). "The Rossiter-McLaughlin Effect of the Transiting Exoplanet XO-4b". Publications of the Astronomical Society of Japan. 62 (6): L61–L65. arXiv:1008.3803. Bibcode:2010PASJ...62L..61N. doi:10.1093/pasj/62.6.l61. S2CID 2967944.
^ ^a ^b Todorov, Kamen O.; et al. (2012). "Warm Spitzer Observations of Three Hot Exoplanets: XO-4b, HAT-P-6b, and HAT-P-8b". The Astrophysical Journal. 746 (1). 111. arXiv:1111.5858. Bibcode:2012ApJ...746..111T. doi:10.1088/0004-637X/746/1/111. S2CID 119200344.

External links

"XO-4". Exoplanets. Archived from the original on 2016-03-03. Retrieved 2009-04-28.

Constellation of Lynx

Stars

Bayer	α ψ¹⁰ Aur (16)
Flamsteed	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 (Alsciaukat) 32 33 34 35 36 38 42 43 44 Cam 45 Cam 46 Cam 48 Cam 50 Cam 52 Cam 54 Cam 5 LMi 10 UMa 19 UMa
Variable	R T U Y RR SW SZ TT TV TZ UU UV UX UY AN BE BF BH BK CC CY DD DI DU
HR	2463 2486 2561 2642 2645 2721 2737 2751 2776 2804 2844 2894 2903 2914 2915 2935 2939 3028 3039 3094 3106 3130 3175 3181 3200 3246 3258 3277 3287 3292 3309 3348 3351 3360 3509 3511 3545 3546 3580 3586 3612 3625 3686 3701 3809
HD	44061 52859 58681 59721 59826 63588 63630 65392 67539 75898 (Stribor)
Other	GD 98 Gliese 277 GJ 1105 GJ 3421 HS 0702+6043 IRC +60169 J0815+4729 PG 0859+415 WASP-13 (Gloas) XO-2 XO-4 (Koit) XO-5 (Absolutno)

Exoplanets	6 Lyncis b WASP-13b (Cruinlagh) XO-2Nb XO-4b (Hämarik) XO-5b (Makropulos)

Star clusters	NGC 2666

Nebulae	Jones-Emberson 1 Lynx Arc

Galaxies

NGC	2273 2273B 2308 2315 2320 2321 2322 2326 2326A 2329 2330 2332 2337 2340 2344 2415 2424 2426 2429 2429A 2429B 2431 2444 2445 2446 2456 2457 2458 2461 2462 2463 2468 2469 2472 2473 2474 2475 2476 2484 2488 2493 2495 2497 2500 2505 2518 2519 2521 2524 2528 2532 2534 2537 2537A 2541 2543 2549 2552 2638 2649 2668 2683 2691 2704 2712 2719 2719A 2724 2746 2755 2759 2770 2776 2778 2779 2780 2782 2785 2793 2798 2799 2823 2825 2826 2827 2828 2829 2830 2831 2832 2833 2834 2838 2839 2840 2844 2852 2853 2860
Other	3C 171 APM 08279+5255 IC 2233 UGC 4653 UGC 4881 UGC 4904

NGC