1025 Riema

1025 Riema, provisional designation 1923 NX, is a bright Hungaria asteroid from the innermost regions of the asteroid belt, approximately 5 kilometers in diameter. It was discovered on 12 August 1923, by German astronomer Karl Reinmuth at the Heidelberg Observatory in southwest Germany.[17] The asteroid was named after ARI astronomer Johannes Riem.[2]

1025 Riema
Discovery [1]
Discovered byK. Reinmuth
Discovery siteHeidelberg Obs.
Discovery date12 August 1923
Designations
(1025) Riema
Named after
Johannes Riem
(German astronomer)[2]
1923 NX · A923 QA
main-belt · (inner)[1] · Hungaria [3][4]
Orbital characteristics [1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc93.81 yr (34,264 days)
Aphelion2.0572 AU
Perihelion1.9009 AU
1.9790 AU
Eccentricity0.0395
2.78 yr (1,017 days)
102.31°
0° 21m 14.4s / day
Inclination26.863°
163.39°
349.06°
Physical characteristics
Dimensions4.605±0.171 km[5]
5.48 km (derived)[3]
3.566±0.005 h[6]
3.578±0.002 h[lower-alpha 1][lower-alpha 2]
3.580±0.005 h[7]
3.581±0.002 h[8][lower-alpha 3]
3.581±0.001 h[9][lower-alpha 2]
3.588±0.002 h[10][lower-alpha 2]
6.557±0.001 h[11]
1.000±0.000[5]
0.166±0.036[12]
0.40 (assumed)[3]
E (Tholen), Xe (SMASS)
M [13] · Xe [3]
B–V = 0.714[1]
U–B = 0.294[1]
V–R = 0.440±0.010[11]
12.30[5] · 12.5[1]
12.57±0.28[14] · 12.92±0.04[3][15][16]

    Orbit and classification

    Riema is a member of the Hungaria family, which form the innermost dense concentration of asteroids in the Solar System. It orbits the Sun at a distance of 1.9–2.1 AU once every 2 years and 9 months (1,017 days). Its orbit has an eccentricity of 0.04 and an inclination of 27° with respect to the ecliptic.[1] The asteroid's observation arc begins at Heidelberg, four nights after its official discovery observation.[17]

    Physical characteristics

    In the Tholen classification, Riema is a bright E-type asteroid. In the SMASS taxonomy, it has been classified as a Xe-type, which transitions from the E to the X-types.[1] In addition, the asteroid has also been polarimetrically characterized as a metallic M-type asteroid.[13]

    Lightcurves

    In August 2001, a first rotational lightcurve of Riema was obtained from photometric observations by Ukrainian astronomers at Kharkiv (101) and Simeiz (094). Lightcurve analysis gave a rotation period of 6.557 hours with a brightness variation of 0.25 magnitude (U=2).[11]

    The Ukrainian team also determined the body's poles and axis-ratios. They found a spin axis of (141.0°, 11.0°) and (321.0.0°, −13.0°) in ecliptic coordinates (λ, β), as well as a semi-axis ratio of 3.41 (a/b) and 1.16 (b/c) for the three-axial ellipsoid model (Q=2).[11]

    Between 2003 and 2017, several additional lightcurves were obtained by American photometrists Robert Stephens and Brian Warner at the Santana Observatory (646), the Palmer Divide Observatory (716) and the Palmer Divide Station (U82), respectively. The constructed lightcurve gave a shorter period for Riema between 3.566 and 3.588 hours with a low amplitude of 0.06 to 0.19 magnitude (U=2/2/2+/2+/3/3).[7][8][9][10][lower-alpha 1][lower-alpha 3][lower-alpha 2]

    Diameter and albedo

    According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Riema measures 4.605 kilometers in diameter and its surface has an outstandingly high albedo of 1.000.[5] The Collaborative Asteroid Lightcurve Link assumes an albedo for E-type Hungaria asteroids of 0.40 – taken from 434 Hungaria, the family's largest member and namesake – and derives a diameter of 5.48 kilometers based on an absolute magnitude of 12.92.[3]

    Naming

    This minor planet was named after Johannes Karl Richard Riem (1868–1945), a German astronomer at the Astronomisches Rechen-Institut (ARI) in Berlin. The name was suggested by ARI. The official naming citation was published by Paul Herget in The Names of the Minor Planets in 1955 (H 98).[2]

    Notes
    1. Warner (2017) web: rotation period 3.578±0.002 hours with a brightness amplitude of 0.06 mag. Summary figures for (1025) Riema at Collaborative Asteroid Lightcurve Link (CALL)
    2. Lightcurve plots by B. D. Warner at the Palmer Divide Station in California: (2014), (2015) and (2017)
    3. Lightcurve plot of 1025 Riema with a period of 3.581±0.002 hours, Palmer Divide Observatory, Colorado, B. D. Warner (2012)

    References
    1. "JPL Small-Body Database Browser: 1025 Riema (1923 NX)" (2017-06-04 last obs.). Jet Propulsion Laboratory. Retrieved 6 July 2017.
    2. Schmadel, Lutz D. (2007). "(1025) Riema". Dictionary of Minor Planet Names – (1025) Riema. Springer Berlin Heidelberg. p. 88. doi:10.1007/978-3-540-29925-7_1026. ISBN 978-3-540-00238-3.
    3. "LCDB Data for (1025) Riema". Asteroid Lightcurve Database (LCDB). Retrieved 6 July 2017.
    4. Spratt, Christopher E. (April 1990). "The Hungaria group of minor planets". Journal of the Royal Astronomical Society of Canada. 84: 123–131. Bibcode:1990JRASC..84..123S. ISSN 0035-872X. Retrieved 6 July 2017.
    5. Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Nugent, C.; et al. (November 2012). "Preliminary Analysis of WISE/NEOWISE 3-Band Cryogenic and Post-cryogenic Observations of Main Belt Asteroids". The Astrophysical Journal Letters. 759 (1): 5. arXiv:1209.5794. Bibcode:2012ApJ...759L...8M. doi:10.1088/2041-8205/759/1/L8. Retrieved 6 July 2017.
    6. Warner, Brian D. (October 2009). "Asteroid Lightcurve Analysis at the Palmer Divide Observatory: 2009 March-June". The Minor Planet Bulletin. 36 (4): 172–176. Bibcode:2009MPBu...36..172W. ISSN 1052-8091. Retrieved 6 July 2017.
    7. Stephens, Robert D. (December 2003). "Photometry of 628 Christine, 754 Malabar, 815 Coppelia, and 1025 Riema". The Minor Planet Bulletin. 30 (4): 69–70. Bibcode:2003MPBu...30...69S. ISSN 1052-8091. Retrieved 6 July 2017.
    8. Warner, Brian D. (January 2013). "Asteroid Lightcurve Analysis at the Palmer Divide Observatory: 2012 June - September". The Minor Planet Bulletin. 40 (1): 26–29. Bibcode:2013MPBu...40...26W. ISSN 1052-8091. Retrieved 6 July 2017.
    9. Warner, Brian D. (January 2016). "Asteroid Lightcurve Analysis at CS3-Palmer Divide Station: 2015 June-September". The Minor Planet Bulletin. 43 (1): 57–65. Bibcode:2016MPBu...43...57W. ISSN 1052-8091. Retrieved 6 July 2017.
    10. Warner, Brian D. (July 2014). "Asteroid Lightcurve Analysis at CS3-Palmer Divide Station: 2014 January-March". The Minor Planet Bulletin. 41 (3): 144–155. Bibcode:2014MPBu...41..144W. ISSN 1052-8091. Retrieved 6 July 2017.
    11. Shevchenko, V. G.; Krugly, Yu. N.; Chiorny, V. G.; Belskaya, I. N.; Gaftonyuk, N. M. (August 2003). "Rotation and photometric properties of E-type asteroids". Planetary and Space Science. 51 (9–10): 525–532. Bibcode:2003P&SS...51..525S. doi:10.1016/S0032-0633(03)00076-X. Retrieved 6 July 2017.
    12. Gil-Hutton, R.; Lazzaro, D.; Benavidez, P. (June 2007). "Polarimetric observations of Hungaria asteroids" (PDF). Astronomy and Astrophysics. 468 (3): 1109–1114. Bibcode:2007A&A...468.1109G. doi:10.1051/0004-6361:20077178. Retrieved 6 July 2017.
    13. Belskaya, I. N.; Fornasier, S.; Tozzi, G. P.; Gil-Hutton, R.; Cellino, A.; Antonyuk, K.; et al. (March 2017). "Refining the asteroid taxonomy by polarimetric observations". Icarus. 284: 30–42. Bibcode:2017Icar..284...30B. doi:10.1016/j.icarus.2016.11.003. Retrieved 6 July 2017.
    14. 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 6 July 2017.
    15. Wisniewski, W. Z.; Michalowski, T. M.; Harris, A. W.; McMillan, R. S. (March 1995). "Photoelectric Observations of 125 Asteroids". Abstracts of the Lunar and Planetary Science Conference. 26: 1511. Bibcode:1995LPI....26.1511W. Retrieved 6 July 2017.
    16. Pravec, Petr; Harris, Alan W.; Kusnirák, Peter; Galád, Adrián; Hornoch, Kamil (September 2012). "Absolute magnitudes of asteroids and a revision of asteroid albedo estimates from WISE thermal observations". Icarus. 221 (1): 365–387. Bibcode:2012Icar..221..365P. doi:10.1016/j.icarus.2012.07.026. Retrieved 6 July 2017.
    17. "1025 Riema (1923 NX)". Minor Planet Center. Retrieved 6 July 2017.

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