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26074 Carlwirtz
Discovery
Discovered by	H.-E. Schuster
Discovery site	La Silla Obs.
Discovery date	8 October 1977
Designations
MPC designation	(26074) Carlwirtz
Named after	Carl Wilhelm Wirtz ; (German astronomer)
Alternative designations	1977 TD · 1996 KH
Minor planet category	Mars-crosser · Hungaria ; binary
Orbital characteristics
	Epoch 27 April 2019 (JD 2458600.5)
	Uncertainty parameter 0
Observation arc	40.83 yr (14,913 d)
Aphelion	1.9722 AU
Perihelion	1.6499 AU
Semi-major axis	1.8110 AU
Eccentricity	0.0890
Orbital period (sidereal)	2.44 yr (890 d)
Mean anomaly	198.66°
Mean motion	0° 24m 15.84s / day
Inclination	31.613°
Longitude of ascending node	102.81°
Argument of perihelion	73.302°
Known satellites	1 (D: n.a. km; P: 16.11 h)
Earth MOID	0.7534 AU (294 LD)
Physical characteristics
Mean diameter	2.54 km (est.); 3.62 km (est.)
Synodic rotation period	2.5493±0.0003 h
Geometric albedo	0.16 (assumed); 0.30 (assumed)
Spectral type	E (assumed)
Absolute magnitude (H)	14.9; 15.0

26074 Carlwirtz (provisional designation 1977 TD) is a dynamical Hungaria asteroid and binary Mars-crosser from the innermost regions of the asteroid belt, approximately 3 kilometers (2 miles) in diameter. It was discovered on 8 October 1977, by German astronomer Hans-Emil Schuster at ESO's La Silla Observatory in northern Chile. The likely binary asteroid on a relatively circular orbit has a short rotation period of 2.5 hours.^[3] It was named for German astronomer Carl Wilhelm Wirtz.^[1] The system's suspected minor-planet moon of unknown size was first detected in 2013.^[5]

Orbit and classification

Carlwirtz is a member of the Mars-crossing asteroids, a dynamically unstable group between the main belt and the near-Earth populations, crossing the orbit of Mars at 1.66 AU.^[1]^[6] It also belongs to the dynamical Hungaria group, which forms the innermost dense concentration of asteroids in the Solar System.^[3] It is, however, not a member of the Hungaria family (003), but a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements.^[6]^[7]

It orbits the Sun in the innermost asteroid belt at a distance of 1.65–1.97 AU once every 2 years and 5 months (890 days; semi-major axis of 1.81 AU). Its orbit has an unusually low eccentricity of 0.09 and an inclination of 32° with respect to the ecliptic.^[2] The body's observation arc begins at La Silla Observatory in October 1977, on the night following its official discovery observation.^[1]

Naming

This minor planet was named after Carl Wilhelm Wirtz (1875–1939), a German astronomer at Strasbourg and Kiel observatories. In 1924, he revealed statistically the redshift-distance relationship of spiral nebulae. The official naming citation was published by the Minor Planet Center on 28 September 2004 (M.P.C. 52769).^[8]

Physical characteristics

Carlwirtz is an assumed E-type asteroid,^[3] but may as well be a common S-type asteroid, since the E-type is typical found among members of the Hungaria family rather than among the larger, encompassing dynamical group with the same name.

Rotation period

In June 2013, a rotational lightcurve of Carlwirtz was obtained from photometric observations by American photometrist Brian Warner at the Palmer Divide Station (U82) in California. Lightcurve analysis gave a well-defined rotation period of 2.5493±0.0003 hours with a brightness amplitude of 0.11±0.01 magnitude (U=3).^[5]^[a] Follow-up observations by Warner in May 2018 gave a similar period 2.539±0.002 hours (U=2+).^[3]^[b]

Satellite

During the observations in June 2013, Warner also noted that Carlwirtz is likely a synchronous binary asteroid with a minor-planet moon in its orbit.^[5]^[a] While the satellite dimension could not be determined, it has an orbital period of 16.11 hours with an estimated semi-major axis of 6.1 kilometers.^[4] However, neither in 2013 nor in the 2018-observations any eclipsing/occultation events could be detected. Instead the asteroid has a classically shaped bimodal lightcurve instead. Since Carlwirtz has a period that is close to two thirds of an Earth-day, single-station observations have difficulties to track a complete lightcurve.^[3]^[5]^[a]^[b]

Diameter and albedo

The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.30 – a compromise value between the S-type (0.20) and E-type (0.40) asteroids – and calculates a diameter of 2.54 kilometers based on an absolute magnitude of 14.9.^[3]^[5] According to estimates by Johnston's archive, Carlwirtz measures 3.62 kilometers in diameter for an assumed albedo of 0.16.

Notes

^ ^a ^b ^c ^d ^e Lightcurve plot of (26074) Carlwirtz Warner (2013), at the Palmer Divide Station (U82). Primary rotation period: 2.5493±0.0003 hours. Secondary rotation period: 16.11±0.02 hours. Quality code is 3. Summary figures at the LCDB and CS3 website.
^ ^a ^b Warner (2018). Lightcurve plot of follow-up observation from May 2018 Quality code is 2+. Summary figures at the LCDB and CS3 website.