984 Gretia

984 Gretia /ˈɡriːtiə/ is a stony background asteroid from the central regions of the asteroid belt, approximately 32 kilometers (20 miles) in diameter. It was discovered by German astronomer Karl Reinmuth at the Heidelberg-Königstuhl State Observatory on 27 August 1922 and given the provisional designation 1922 MH.[17] The asteroid was named after Greta, sister-in-law of ARI-astronomer Albrecht Kahrstedt.[17]

984 Gretia
3D-model of Gretia based on its lightcurve
Discovery [1]
Discovered byK. Reinmuth
Discovery siteHeidelberg Obs.
Discovery date27 August 1922
Designations
(984) Gretia
Pronunciation/ˈɡriːtiə/
Named after
Greta, sister-in-law of astronomer Albrecht Kahrstedt [2]
1922 MH · 1973 LC
A910 BA · A915 DA
main-belt · (middle)
background
Orbital characteristics [1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc94.45 yr (34,499 days)
Aphelion3.3562 AU
Perihelion2.2495 AU
2.8028 AU
Eccentricity0.1974
4.69 yr (1,714 days)
65.271°
0° 12m 36s / day
Inclination9.0930°
314.21°
55.494°
Physical characteristics
Dimensions31.91±3.1 km[3][4]
32.449±0.306 km[5]
34.91±0.47 km[6]
36.600±0.187 km[7]
5.560±0.018 h[8]
5.76 h[9]
5.778±0.001 h[10]
5.778026±0.000001 h[11]
5.77827±0.00005 h[10]
5.7789±0.0002 h[12]
5.780±0.001 h[13]
5.781 h[14][15]
0.3566±0.0863[7]
0.360±0.012[6]
0.421±0.038[5]
0.4239±0.095[3]
SMASS = Sr [1] · S [4]
B–V = 0.950±0.030[8]
9.03[1][3][4][6][7] · 9.52±0.16[16]

    Orbit and classification

    Gretia is a background asteroid that has not been associated with any known asteroid family. It orbits the Sun in the central main belt at a distance of 2.2–3.4 AU once every 4 years and 8 months (1,714 days). Its orbit has an eccentricity of 0.20 and an inclination of 9° with respect to the ecliptic.[1]

    It was first observed as A910 BA at the discovering observatory in 1910, and five years later as A915 DA at the United States Naval Observatory. The body's observation arc begins at Vienna Observatory in September 1922, two weeks after its official discovery observation.[17]

    Naming

    This minor planet was named after Greta, sister-in-law of Albrecht Kahrstedt (1897–1971), a German astronomer at ARI and director of the institute's Potsdam division, who requested the naming of this asteroid and 1026 Ingrid (daughter of Greta) in a personal letter to the discoverer in February 1926.[2][18] Kahrstedt himself was honored with the naming of 1587 Kahrstedt.

    The official naming citation was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 94).[2] Lutz Schmadel quoted an excerpt of Kahrstedt's letter in his Dictionary of Minor Planet Names (LDS).[18]

    Physical characteristics

    In the SMASS classification, Gretia is a Sr-subtype that transitions between the common S-type and rare R-type asteroids.[1]

    Lightcurves

    Since 1997, a large number of rotational lightcurves of Gretia have been obtained from photometric observations. Analysis of the best-rated lightcurves gave a rotation period of 5.778 hours with a maximal brightness amplitude from 0.26 to 0.75 magnitude (U=2–3).[8][9][10][11][12][13][14][15]

    The asteroid's spin axis of (92.0°, 67.0°) and (247.0°, 48.0°) in ecliptic coordinates (λ, β) have also been derived from modeled lightcurves (Q=3).[11]

    Diameter and albedo

    According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Gretia measures between 31.91 and 36.60 kilometers in diameter and its surface has a high albedo between 0.3566 and 0.4239.[3][5][6][7]

    The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an exceptionally high albedo of 0.4239 and a diameter of 31.91 kilometers with an absolute magnitude of 9.03.[3][4]

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    References
    1. "JPL Small-Body Database Browser: 984 Gretia (1922 MH)" (2017-02-08 last obs.). Jet Propulsion Laboratory. Retrieved 26 August 2017.
    2. Schmadel, Lutz D. (2007). "(984) Gretia". Dictionary of Minor Planet Names – (984) Gretia. Springer Berlin Heidelberg. p. 85. doi:10.1007/978-3-540-29925-7_985. ISBN 978-3-540-00238-3.
    3. Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 22 October 2019.
    4. "LCDB Data for (984) Gretia". Asteroid Lightcurve Database (LCDB). Retrieved 26 August 2017.
    5. Masiero, Joseph R.; Grav, T.; Mainzer, A. K.; Nugent, C. R.; Bauer, J. M.; Stevenson, R.; et al. (August 2014). "Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos". The Astrophysical Journal. 791 (2): 11. arXiv:1406.6645. Bibcode:2014ApJ...791..121M. doi:10.1088/0004-637X/791/2/121. Retrieved 26 August 2017.
    6. Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. Retrieved 17 October 2019. (online, AcuA catalog p. 153)
    7. Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90.
    8. Riccioli, D.; Blanco, C.; Cigna, M. (June 2001). "Rotational periods of asteroids II". Planetary and Space Science. 49 (7): 657–671. Bibcode:2001P&SS...49..657R. doi:10.1016/S0032-0633(01)00014-9. Retrieved 26 August 2017.
    9. van Houten, C. J. (March 1962). "An investigation of asteroid light-curves on Franklin-Adams plates". Bulletin of the Astronomical Institutes of the Netherlands. 16: 160. Bibcode:1962BAN....16..160V. Retrieved 26 August 2017.
    10. Behrend, Raoul. "Asteroids and comets rotation curves – (984) Gretia". Geneva Observatory. Retrieved 26 August 2017.
    11. Marciniak, A.; Michalowski, T.; Kwiatkowski, T.; Kamínski, K. (December 2007). "Modelling Asteroids' Shapes Based on Their Lightcurves". Asteroids. 1405: 8129. Bibcode:2008LPICo1405.8129M. Retrieved 26 August 2017.
    12. Schmidt, Richard E. (July 2017). "Near-IR Minor Planet Photometry from Burleith Observatory". The Minor Planet Bulletin. 44 (3): 191–192. Bibcode:2017MPBu...44..191S. ISSN 1052-8091. Retrieved 26 August 2017.
    13. Gandolfi, D.; Cigna, M.; Fulvio, D.; Blanco, C. (January 2009). "CCD and photon-counting photometric observations of asteroids carried out at Padova and Catania observatories". Planetary and Space Science. 57 (1): 1–9. arXiv:0810.1560. Bibcode:2009P&SS...57....1G. doi:10.1016/j.pss.2008.09.014. Retrieved 26 August 2017.
    14. di Martino, M. (December 1984). "Physical study of asteroids - Lightcurves and rotational periods of six asteroids". Icarus. 60 (3): 541–546.ResearchsupportedbytheConsiglioNazionaledelleRicerche. Bibcode:1984Icar...60..541D. doi:10.1016/0019-1035(84)90162-3. ISSN 0019-1035. Retrieved 26 August 2017.
    15. Piironen, J.; Bowell, E.; Erikson, A.; Magnusson, P. (September 1994). "Photometry of eleven asteroids at small phase angles". Astronomy and Astrophysics Supplement. 106: 587. Bibcode:1994A&AS..106..587P. Retrieved 26 August 2017.
    16. Veres, Peter; Jedicke, Robert; Fitzsimmons, Alan; Denneau, Larry; Granvik, Mikael; Bolin, Bryce; et al. (November 2015). "Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 - Preliminary results". Icarus. 261: 34–47. arXiv:1506.00762. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007. Retrieved 26 August 2017.
    17. "984 Gretia (1922 MH)". Minor Planet Center. Retrieved 26 August 2017.
    18. Schmadel, Lutz D. (2007). "(1026) Ingrid". Dictionary of Minor Planet Names – (1026) Ingrid. Springer Berlin Heidelberg. p. 88. doi:10.1007/978-3-540-29925-7_1027. ISBN 978-3-540-00238-3.

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