21795 Masi

21795 Masi, provisional designation 1999 SN9, is a Nysian asteroid from the inner regions of the asteroid belt, approximately 3 kilometers (2 miles) in diameter. It was discovered on 29 September 1999, by Italian amateur astronomer Franco Mallia at the Campo Catino Astronomical Observatory in Lazio, Italy.[1] The likely S-type asteroid has a rotation period of 13.86 hours.[4] It was named for Italian astronomer Gianluca Masi.[1]

21795 Masi
Discovery [1]
Discovered byF. Mallia
Discovery siteCampo Catino Obs.
Discovery date29 September 1999
Designations
(21795) Masi
Named after
Gianluca Masi [1]
(Italian astronomer)
1999 SN9 · 1988 UE
1993 BZ1
main-belt [1][2] · (inner)
Nysa [3]
Orbital characteristics [2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc64.45 yr (23,541 d)
Aphelion2.8409 AU
Perihelion1.9222 AU
2.3815 AU
Eccentricity0.1929
3.68 yr (1,342 d)
337.35°
0° 16m 5.52s / day
Inclination1.8376°
337.09°
81.681°
Physical characteristics
Mean diameter
2.45 km (calculated)[4]
3.150±0.164 km[5][6]
13.862±0.0121 h[7]
0.20 (assumed)[4]
0.235±0.037[5][6]
S (assumed)[4]
14.7[6]
14.9[2]
14.970±0.004 (R)[7]
15.41±0.14[8]
15.42[4]

    Orbit and classification

    Masi is member of the Nysa family (405),[3] located in the Nysa–Polana complex and one of the largest asteroid families of the asteroid belt, named after 44 Nysa.[9] It orbits the Sun in the inner main-belt at a distance of 1.9–2.8 AU once every 3 years and 8 months (1,342 days; semi-major axis of 2.38 AU). Its orbit has an eccentricity of 0.19 and an inclination of 2° with respect to the ecliptic.[2] The body's observation arc begins with a precovery published by the Digitized Sky Survey and taken at the Palomar Observatory in April 1954, more than 45 years prior to its official discovery observation at Campo Catino.[1]

    Physical characteristics

    Masi is an assumed, stony S-type asteroid,[4] which is also the overall spectral type for members of the Nysa family of asteroids.[9]:23

    Rotation period

    In September 2010, a rotational lightcurve of Masi was obtained from photometric observations in the R-band by astronomers at the Palomar Transient Factory in California. Lightcurve analysis gave a rotation period of 13.862 hours with a relatively high brightness amplitude of 0.68 magnitude (U=2).[7]

    Diameter and albedo

    According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Masi measures 3.150 kilometers in diameter and its surface has an albedo of 0.235,[5][6] while the Collaborative Asteroid Lightcurve Link assumes a standard albedo for a stony asteroid of 0.20, and calculates a diameter of 2.45 kilometers based on an absolute magnitude of 15.42.[4]

    Naming

    This minor planet was named after Italian astrophysicist and astronomer, Gianluca Masi (born 1972), a researcher and discoverer of minor planets and variable stars, who became an avid amateur astronomer when he was 8 years old.[1] The official naming citation was published by the Minor Planet Center on 9 May 2001 (M.P.C. 42679).[10]

    References
    1. "21795 Masi (1999 SN9)". Minor Planet Center. Retrieved 29 May 2018.
    2. "JPL Small-Body Database Browser: 21795 Masi (1999 SN9)" (2017-09-27 last obs.). Jet Propulsion Laboratory. Retrieved 29 May 2018.
    3. "Asteroid 21795 Masi". Small Bodies Data Ferret. Retrieved 29 May 2018.
    4. "LCDB Data for (21795) Masi". Asteroid Lightcurve Database (LCDB). Retrieved 29 May 2018.
    5. Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Dailey, J.; et al. (November 2011). "Main Belt Asteroids with WISE/NEOWISE. I. Preliminary Albedos and Diameters". The Astrophysical Journal. 741 (2): 20. arXiv:1109.4096. Bibcode:2011ApJ...741...68M. doi:10.1088/0004-637X/741/2/68.
    6. 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. (catalog)
    7. Waszczak, Adam; Chang, Chan-Kao; Ofek, Eran O.; Laher, Russ; Masci, Frank; Levitan, David; et al. (September 2015). "Asteroid Light Curves from the Palomar Transient Factory Survey: Rotation Periods and Phase Functions from Sparse Photometry". The Astronomical Journal. 150 (3): 35. arXiv:1504.04041. Bibcode:2015AJ....150...75W. doi:10.1088/0004-6256/150/3/75.
    8. 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.
    9. Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). Identification and Dynamical Properties of Asteroid Families. Asteroids IV. pp. 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. ISBN 9780816532131.
    10. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 29 May 2018.

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