{
  "abstract": "We present photometric, spectroscopic, and polarimetric observations of (163693) Atira collected on the night of 05 March 2024. A dual-band lightcurve acquired in the V and R_C filters using the Metsähovi Observatory (L08) in Kirkkonummi, Finland spans nearly 8~hours. From these measurements we estimate a V-R_C = 0.43 +/- 0.07 mag. A visible spectrum and linear polarisation measurement were obtained with the Nordic Optical Telescope in La Palma, Spain. We employ a semi-empirical model to recover the spectral flux that was lost due to a mis-aligned spectroscopic slit. The corrected model reflectance spectrum indicates a primitive Cgh taxonomic type with a distinct absorption feature from 0.60 to 0.85 um with a depth of ~7.4 %. Direct comparison with laboratory spectra of meteorites indicates close matches with CM carbonaceous chondrites. We detect a large degree of linear polarisation at a phase angle of 83 degrees which is consistent with (3200) Phaethon and (155140) 2005 UD, but lower than (162173) Ryugu and (152679) 1998 KU2. We use a CM carbonaceous chondrite density to estimate its bulk porosity of 51 +/- 31 % from previously estimated bulk density. The uncertainty in bulk density and bulk porosity is dominated by the volume of the primary. Future near-infrared spectroscopic and thermal infrared observations can be used to refine the composition and bulk density. Finally, we discuss implications for ground-based physical characterisation studies of the Atira population.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.27722",
  "author_total": 8,
  "authors": [
    {
      "name": "Eric M. MacLennan"
    },
    {
      "name": "Grigori Fedorets"
    },
    {
      "name": "Zuri Gray"
    },
    {
      "name": "Teemu Willamo"
    },
    {
      "name": "Tuomas Salo"
    },
    {
      "name": "Anne Virkki"
    },
    {
      "name": "Mikael Granvik"
    },
    {
      "name": "Karri Muinonen"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/9a2pwpjec1w4c.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.27722",
  "fulltext_url": null,
  "id": "9a2pwpjec1w4c",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.27722",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "openalex",
      "3103|Astro and Planetary Science"
    ]
  ],
  "openalex": "W7214238998",
  "pdf_url": "https://arxiv.org/pdf/2609.27722",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-23",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/9a2pwpjec1w4c.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:56Z",
      "native_id": "2609.27722",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.27722"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "Nordic-based observations of binary asteroid (163693) Atira reveal a hydrated CM chondrite composition",
  "title_text": "Nordic-based observations of binary asteroid (163693) Atira reveal a hydrated CM chondrite composition",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:56Z",
  "url": "https://research.draconitic.com/paper/9a2pwpjec1w4c",
  "venue": "arXiv",
  "versions": []
}