A high geometric albedo and small size for the Haumea cluster member (24835) 1995 SM ₅₅ determined from a stellar occultation and photometric observations

@article{ortiz2026high,
  title = {{A high geometric albedo and small size for the Haumea cluster member (24835) 1995 SM ₅₅ determined from a stellar occultation and photometric observations}},
  author = {J L Ortiz and N Morales and B Sicardy and F L Rommel and F Braga-Ribas and Y Kilic and E Fernández-Valenzuela and J L Rizos and B Morgado and L Catani and M Kretlow and J M Gómez-Limón and J Desmars and P Santos-Sanz and O Erece and I Akoz and K Uluc and S Kaspi and A Marciniak and V Turcu and D Moldovan and A Sonka and E Petrescu and A Nedelcu and C Nehir and R Morales and R Duffard and D Souami and W Thuillot and J I B Camargo and R Vieira-Martins and J Lecacheux and A Alvarez-Candal and M Assafin and G Benedetti-Rossi and A Gomes-Junior and R Boufleur and U Hopp and C Goessl and M Schmidt and A Takey and A M Abdelaziz and H Mikuz and A Mohar and J Skvarc and O Schreurs and M Lecossois and T Janik and M N Bagiran and S Fişek and S Alis and F K Yelkenci and M Acar and N Takacs and R Szakats and A Pal and J Manek and B A Dumitru and K Gazeas and F Ursache},
  journal = {Astronomy \& Astrophysics - A\&A},
  year = {2026},
  month = oct,
  doi = {10.1051/0004-6361/202556498},
  url = {https://hal-obspm.ccsd.cnrs.fr/obspm-05805882v1},
  note = {CC BY 4.0},
}

TY  - JOUR
TI  - A high geometric albedo and small size for the Haumea cluster member (24835) 1995 SM ₅₅ determined from a stellar occultation and photometric observations
AU  - J L Ortiz
AU  - N Morales
AU  - B Sicardy
AU  - F L Rommel
AU  - F Braga-Ribas
AU  - Y Kilic
AU  - E Fernández-Valenzuela
AU  - J L Rizos
AU  - B Morgado
AU  - L Catani
AU  - M Kretlow
AU  - J M Gómez-Limón
AU  - J Desmars
AU  - P Santos-Sanz
AU  - O Erece
AU  - I Akoz
AU  - K Uluc
AU  - S Kaspi
AU  - A Marciniak
AU  - V Turcu
AU  - D Moldovan
AU  - A Sonka
AU  - E Petrescu
AU  - A Nedelcu
AU  - C Nehir
AU  - R Morales
AU  - R Duffard
AU  - D Souami
AU  - W Thuillot
AU  - J I B Camargo
AU  - R Vieira-Martins
AU  - J Lecacheux
AU  - A Alvarez-Candal
AU  - M Assafin
AU  - G Benedetti-Rossi
AU  - A Gomes-Junior
AU  - R Boufleur
AU  - U Hopp
AU  - C Goessl
AU  - M Schmidt
AU  - A Takey
AU  - A M Abdelaziz
AU  - H Mikuz
AU  - A Mohar
AU  - J Skvarc
AU  - O Schreurs
AU  - M Lecossois
AU  - T Janik
AU  - M N Bagiran
AU  - S Fişek
AU  - S Alis
AU  - F K Yelkenci
AU  - M Acar
AU  - N Takacs
AU  - R Szakats
AU  - A Pal
AU  - J Manek
AU  - B A Dumitru
AU  - K Gazeas
AU  - F Ursache
PY  - 2026
DA  - 2026/10/19
JO  - Astronomy & Astrophysics - A&A
DO  - 10.1051/0004-6361/202556498
UR  - https://hal-obspm.ccsd.cnrs.fr/obspm-05805882v1
AB  - Context. Trans-Neptunian objects (TNOs) are thought to be some of the most ancient and primitive bodies in our Solar System. Understanding their basic physical properties is crucial to unraveling their origin and the evolution of the outer Solar System beyond Neptune. Stellar occultations are a highly effective and sensitive method of studying these distant and faint objects, allowing us to gather essential information about their physical characteristics. (24835) 1995 SM 55 is one of the few members of the Haumea orbital cluster and, therefore, is an especially relevant body to study within the TNO population. Aims. The main objectives of the present work are to determine the projected size, absolute magnitude, and geometric albedo of 1995 SM 55 and to analyze the results compared to Haumea. Methods. We predicted a stellar occultation by this TNO for February, 25, 2024, carried out a specific campaign to observe the occultation, and derived the projected size and shape from the occultation observations using an elliptical fit to the occultation chords. We also analyzed a large set of photometric observations of (24835) 1995 SM 55 to obtain the absolute magnitude and the rotational period. Finally, we combined these results to derive the geometric albedo of this TNO. Results. The occultation was successfully detected from seven instruments located at five different sites; 33 other sites reported negative detections. Using an elliptical fit to the occultation chords, we determined the size and shape of the limb of ( 24835) 1995 SM 55 during the occultation: an ellipse with semi-axes (104.3 ± 0.4) × (83.5 ± 0.5) km. The area-equivalent diameter (D eq,A ) for this ellipse is 186.7 ± 1.8 km. This is consistent with the upper limit of 250 km estimated from Herschel Observatory thermal data. From our photometric observations, we derived an absolute magnitude (H V ) of 4.55 ± 0.03, a phase slope parameter of 0.04 ± 0.02 mag/deg, and a V -R value of 0.37 ± 0.05. The rotational variability has a maximum peak-to-valley amplitude (∆m) of 0.05 mag, but we could not derive an unambiguous rotational period. Combining the projected size from the occultation with the absolute photometry, we obtained a geometric albedo in the V band (p V ) of 0.80 ± 0.04 for 1995 SM 55 . This value is remarkably high for a TNO and somewhat higher than that of Haumea, but consistent with the concept that 1995 SM 55 is a member of the orbital cluster of Haumea.
SN  - 0004-6361
SN  - 1432-0746
ER  -