| Minorplanet: | yes |
| 794 Irenaea | |
| Background: |
|
| Discovery Ref: |   |
| Discovered: | 27 August 1914 |
| Mpc Name: | (794) Irenaea |
| Alt Names: | A914 QB1930 KH 1936 QK1947 QD 1914 VB |
| Named After: | Irene Hillebrand, daughter of Edmund Weiss |
| Mp Category: |
|
| Orbit Ref: |   |
| Epoch: | 31 May 2020 (JD 2459000.5) |
| Uncertainty: | 0 |
| Observation Arc: | 83.12 yr (30,360 d) |
| Perihelion: | 2.2004 AU |
| Semimajor: | 3.1281 AU |
| Eccentricity: | 0.2966 |
| Period: | 5.53 yr (2,021 d) |
| Mean Motion: | / day |
| Inclination: | 5.4193° |
| Asc Node: | 160.40° |
| Arg Peri: | 131.27° |
| Mean Diameter: | |
| Albedo: | |
| Abs Magnitude: |
|
794 Irenaea (prov. designation: or) is a dark background asteroid from the outer regions of the asteroid belt. It was discovered on 27 August 1914, by Austrian astronomer Johann Palisa at the Vienna Observatory. The presumed C-type asteroid has a rotation period of 9.1 hours and measures approximately 36km (22miles) in diameter. It was likely named after Irene Hillebrand, daughter of Austrian astronomer Edmund Weiss (1837–1917).
Irenaea is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements. It orbits the Sun in the outer main-belt at a distance of 2.2–4.1 AU once every 5 years and 6 months (2,021 days; semi-major axis of 3.13 AU). Its orbit has an eccentricity of 0.30 and an inclination of 5° with respect to the ecliptic. The body's observation arc begins at Bergedorf Observatory in Hamburg on 9 December 1915, more than a year after its official discovery observation at Vienna Observatory on 27 August 1914.
According to Alexander Schnell, this minor planet was likely named after Irene Hillebrand, née Weiss, daughter of Austrian astronomer Edmund Weiss (1837–1917), director of the Vienna Observatory, and wife to astronomer (1861–1939). The name received an aea-suffix as "Irene" was already given to asteroid 14 Irene. Palisa also named asteroid 722 Frieda after her daughter, Frieda Hillebrand.
Irenaea is an assumed, carbonaceous C-type asteroid. The asteroid's low albedo around 0.05 (see below) agrees with this assumption.
In May 2008, a rotational lightcurve of Irenaea was obtained from photometric observations by Italian amateur astronomer Silvano Casulli. Lightcurve analysis gave a rotation period of hours with a brightness variation of magnitude, indicative of an elongated shape .
According to the surveys carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), the Infrared Astronomical Satellite IRAS, and the Japanese Akari satellite, Irenaea measures, and kilometers in diameter and its surface has an albedo of, and, respectively. The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous C-type asteroid of 0.057 and calculates a diameter of 30.59 kilometers based on an absolute magnitude of 11.3. Alternative mean diameter measurements published by the WISE team include, and with corresponding albedos of, and .
}