511 Davida

511 Davida is a large C-type asteroid in the asteroid belt. It is one of the largest asteroids; approximately tied for 7th place, to within measurement uncertainties, and the 5th or 6th most massive. It was discovered by R. S. Dugan in 1903. Davida is named after David Peck Todd, an astronomy professor at Amherst College.

511 Davida

Discovery
Discovered by	R. S. Dugan
Discovery date	May 30, 1903
Designations
Designation	(511) Davida
Pronunciation	/dəˈviːdə/,[1] Latin Dāvīda
Named after	David Peck Todd
Alternative names	1903 LU
Minor planet category	main-belt · (outer) Meliboea [2]
Adjectives	Davidian /dəˈvɪdiən/[3]
Orbital characteristics[4]
Epoch July 01, 2021 (JD 2459396.5, heliocentric)
Aphelion	3.759 AU
Perihelion	2.569 AU
Semi-major axis	3.163 AU
Eccentricity	0.188
Orbital period (sidereal)	5.626 yr (2055 d)
Mean anomaly	113°
Inclination	15.94°
Longitude of ascending node	107.6°
Argument of perihelion	337.2°
Physical characteristics
Dimensions	(357 ± 2) × (294 ± 2) × (231 ± 50) km[6][a]
Mean diameter	298±4 km[7]
Flattening	0.30[b]
Mass	(26.6±7.3)×1018 kg[7] (38±2)×1018 kg[c][5]
Mean density	1.92±0.53 g/cm3[7] 2.97±1.30 g/cm3[5]
Synodic rotation period	0.2137 d (5.130 h)
Albedo	0.076±0.007 geometric (0.717±0.013 BV, 0.363±0.020)[4]
Temperature	~160 K
Spectral type	C
Apparent magnitude	9.50[8] to 12.98
Absolute magnitude (H)	6.43[4]

Physical characteristics

Asteroid 511 Davida (lower left at mag 12.5) near galaxy NGC 5792

3D model of Davida based on lightcurve modeling

Keck telescope image sequence of Davida showing its rotation

Davida is approximately 270–310 km in diameter and comprises an estimated 1.5% of the total mass of the asteroid belt.^[9][10][d] It is a C-type asteroid, which means that it is dark in colouring with a carbonaceous chondrite composition.

From 2002 to 2007, astronomers at the Keck Observatory used the Keck II telescope, which is fitted with adaptive optics, to photograph Davida. The asteroid is not a dwarf planet: there are at least two promontories and at least one flat facet with 15-km deviations from a best-fit ellipsoid. The facet is presumably a 150-km global-scale crater like the ones seen on 253 Mathilde. Conrad et al. (2007) show that craters of this size "can be expected from the impactor size distribution, without likelihood of catastrophic disruption of Davida."

Mass

In 2001, Michalak estimated Davida to have a mass of (6.64±0.56)×10¹⁹ kg.^[11][e] In 2007, Baer and Chesley estimated Davida to have a mass of (5.9±0.6)×10¹⁹ kg.^[12] As of 2010^[update], Baer suggests Davida has a mass of (3.84±0.20)×10¹⁹ kg.^[9] This most recent estimate by Baer indicates that Davida is approximately tied with 704 Interamnia as the fifth-most-massive asteroid, though the error bars of Interamnia are large.^[9]

Occultations

There have been 9 occultation events observed since 1987, many of which produced two or three chords.^[13] Two examples shown here.

Occultations by 511 Davida: Left: Double chord occultation of TYC 5597-01223 on 5 August 2016, observed by two amateur astronomers in eastern Australia. Both observers noted step events, thereby detecting the star has two components. Right: Triple chord occultation of TYC 1964-00787, observed on 6 February 2009 by three astronomers in eastern United States.

511 Davida occulted TYC 5597-01223 on 5 August 2016. Two observers recorded the event and both observed step events. Shown here is the step recording by Dave Herald.

Notes

1. Measurements of the short axis are less precise than the other two, but also involve a discrepancy between fitting the convolved and deconvolved images (241±40 km), and fitting the edges (191±114 km).
2. Flattening derived from the maximum aspect ratio (c/a): ${\displaystyle f=1-{\frac {c}{a}}}$, where (c/a) = 0.70±0.06.^[7]
3. (18.96 ± 0.99) × 10⁻¹² M_☉
4. "Baer Mass of 511 Davida" 0.220 / "Mass of Mbelt" 15 = 0.0146
5. (3.34±0.28)×10⁻¹¹ solar masses, per Michalak (2001), extended dynamic model.