CONSTRAINTS ON THE PRESENCE OF SiO GAS IN THE DEBRIS DISK OF HD 172555

Abstract

We have carried out two sets of observations to quantify the properties of SiO gas in the unusual HD 172555 debris disk: (1) a search for the J=8-7 rotational transition from the vibrational ground state, carried out with the Atacama Pathfinder EXperiment (APEX) submillimeter telescope and heterodyne receiver at 863 μmand (2) a search at 8.3 μm for the P(17) ro-vibrational transition of gas phase SiO, carried out with the Very Large Telescope (VLT)/VISIR with a resolution, λ/Δλ, of 30,000. The APEX measurement resulted in a 3.3σ detection of an interstellar feature, but only an upper limit to emission at the radial velocity and line width expected from HD 172555. The VLT/VISIR result was also an upper limit. These were used to provide limits for the abundance of gas phase SiOfor a range of temperatures. The upper limit from our APEX detection, assuming an 8000 K primary star photospheric excitation, falls more than an order of magnitude below the self-shielding stability threshold derived by Johnson et al. (2012). Our results thus favor a solid-state origin for the 8.3 μm feature seen in the Spitzer IRS spectrum of the circumstellar excess emissionand the production of circumstellar O I and Si I by SiO UV photolysis. The implications of these estimates are explored in the framework of models of the HD 172555 circumstellar disk.

Detection of scattered light from the hot dust in HD 172555

“…HD 172555 (HIP 92024, HR 7012) is one of the most studied objects among these special stellar systems (Cote 1987;Schütz et al 2005;Chen et al 2006;Wyatt et al 2007b;Lisse et al 2009;Smith et al 2012;Riviere-Marichalar et al 2012; Article number, page 1 of 16 arXiv:1808.04373v1 [astro-ph.EP] 13 Aug 2018 A&A proofs: manuscript no. HD172555_v7_arxiv Johnson et al 2012;Kiefer et al 2014;Wilson et al 2016;Grady et al 2018).…”

“…Aside from this, several stars with hot disks have been found (Wyatt et al 2007a;Fujiwara et al 2009) based on the IR excess with an estimate temperature above 300 K. The stars that possess hot dust are very interesting targets because the submicron-sized grains at a small small distance from a star could be a signpost for transient collision events. HD 172555 (HIP 92024, HR 7012) is one of the most studied objects among these special stellar systems (Cote 1987;Schütz et al 2005;Chen et al 2006;Wyatt et al 2007b;Lisse et al 2009;Smith et al 2012;Riviere-Marichalar et al 2012;Johnson et al 2012;Kiefer et al 2014;Wilson et al 2016;Grady et al 2018).…”

HD 145263: Spectral Observations of Silica Debris Disk Formation via Extreme Space Weathering?

“…A strong signature of 'SiO gas' is also present. However, since Lisse 2009, studies by Johnson et al 2012 andWilson et al 2016 cast some doubt on the presence of this species, both from a photolytic stability and an actual measurement standpoint. The amorphous silicates/silica study of Speck et al 2011, and the Mars Spirit rover study of Ruff et al 2011 have demonstrated that this 8 µm shoulder feature may be a solid state feature found in hydrated forms of silica like hyalite (but not unhydrated forms like obsidian, cristobolite, or tektite).…”

The Star-grazing Bodies in the HD 172555 System

“…Lisse et al (2009) suggested the presence of silica emission in mid-IR spectra of HD 172555, as the parent molecule for atomic oxygen. This interpretation has subsequently been questioned (Wilson et al 2016). If vaporized and photodissociated, SiO dissociation should produce silicon and oxygen ion profiles that closely resemble each other.…”