J/ApJ/866/L1 Dust models & IR spectroscopy obs. of AGB stars (Sargent, 2018) ================================================================================ Alumina polymorphism in the circumstellar dust shells of asymptotic giant branch stars. Sargent B.A. =2018ApJ...866L...1S ================================================================================ ADC_Keywords: Spectra, infrared; Stars, giant; Models; Interstellar medium Keywords: circumstellar matter ; infrared: stars Abstract: Many emission features remain unidentified in the infrared spectra of asymptotic giant branch (AGB) stars. In particular, features at ~11, 20, 28, and 32{mu}m have been noted in mid-infrared spectra of oxygen-rich AGB stars. Here, I present models of dust excess emission in 36 spectra of 24 AGB stars from the Short Wavelength Spectrometer on board the Infrared Space Observatory and the Infrared Spectrograph on the Spitzer Space Telescope. The models include opacities of grains composed of mixtures of various polymorphs of alumina obtained by preparing bayerite and boehmite at high temperatures, and these dust components provide satisfactory fits to the 11, 20, 28, and 32{mu}m features. Though not a direct conclusion from this study, the presence of grains of the various polymorphs of aluminas in circumstellar dust shells around AGB stars suggests that corundum may have a role in giving rise to the 13{mu}m feature. Description: The spectra analyzed in this study come both from the Spitzer Space Telescope Infrared Spectrograph (IRS) and from the Infrared Space Observatory (ISO) Short Wavelength Spectrometer (SWS). My sample of spectra were chosen from among previous studies of AGB stars (see Table 1) for their relatively prominent 11, 20, 28, and 32um emission features. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file sample.dat 16 24 List of the stars; table added by CDS table1.dat 197 72 Sample information and dust model parameters -------------------------------------------------------------------------------- See also: I/345 : Gaia DR2 (Gaia Collaboration, 2018) J/A+AS/146/437 : IR spectra of oxygen-rich evolved stars (Speck+, 2000) J/A+A/442/281 : Late-type giants BVRIJHKL & Teff calib. (Kucinskas+, 2005) J/A+A/483/661 : Refractive index for silicon carbide (SiC) (Pitman+, 2008) J/ApJ/693/L81 : Extinction in star-forming regions (McClure, 2009) J/ApJS/193/23 : Fundamental stellar parameters in 47 Tucanae (McDonald+, 2011) J/A+A/553/A81 : Refraction of corundum, spinel, {alpha}-quartz (Zeidler+, 2013) J/ApJ/811/45 : Infrared spectral properties of M giants (Sloan+, 2015) J/A+A/592/A42 : A study of dust nucleation in Mira. Part I. (Kaminski+, 2016) Byte-by-byte Description of file: sample.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 16 A16 --- ID Target identifier -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 16 A16 --- ID Target identifier 18 A1 --- r_ID [abcdef] Flag on ID (1) 20- 23 F4.2 kpc Dist [0.1/7.8]? Distance (2) 25 A1 --- f_Dist [ghij] Flag on Dist (3) 27- 31 F5.3 mag Av [0.01/1.6]? V band extinction (4) 33 A1 --- f_Av [ghij] Flag on Av (3) 35- 45 A11 --- Inst Spitzer/IRS or ISO/SWS instrument 47- 54 I8 --- AOR Spitzer AOR or ISO AOT data identifier 56- 77 A22 --- ModScl Module scalars (5) 79- 82 I4 K Temp [56/1400] Model dust temperature 84- 93 E10.2 g/cm2 AmEn [0/3.5e-14] Amorphous Enstatite mass weight (6) 95-104 E10.2 g/cm2 e_AmEn [1.5e-22/1.4e-14] Uncertainty in AmEn 106-114 E9.2 g/cm2 Cor [0/1.2e-13] Corundum mass weight (6) 116-124 E9.2 g/cm2 e_Cor [3e-23/1.4e-13] Uncertainty in Cor 126-135 E10.2 g/cm2 Bayer [0/1.2e-14] "Bayerite 1273K" mass weight (6)(7) 137-145 E9.2 g/cm2 e_Bayer [5.8e-23/8.5e-16] Uncertainty in Bayer 147-156 E10.2 g/cm2 AmAl [0/2.4e-14] Amorphous Alumina mass weight (6) 158-165 E8.2 g/cm2 e_AmAl [9.5e-23/5.5e-15] Uncertainty in AmAl 167-176 E10.2 g/cm2 Boe [0/3.8e-14] "Boehmite 1173K" mass weight (6)(7) 178-186 E9.2 g/cm2 e_Boe [7.3e-23/2.2e-15] Uncertainty in Boe 188-197 F10.5 --- Chi2 [0.8/1704]? Model {Chi}^2^/degrees of freedom value determined over 8.0<{lambda}<37um -------------------------------------------------------------------------------- Note (1): Flag as follows: a = Sources from Smolders+ (2012A&A...540A..72S); b = Sources from Sloan+ (2003ApJ...594..483S); c = Source from McDonald+ (2011MNRAS.417...20M); d = Sources from Lebzelter+ (2006ApJ...653L.145L); e = Sources from Sloan+ (2010ApJ...719.1274S); f = Source from Olofsson+ (2009A&A...507..327O). Note (2): From parallaxes reported by GAIA DR2 (Gaia Collaboration 2016A&A...595A...2G ; Arenou+ 2018A&A...616A..17A Gaia Collaboration 2018A&A...616A...1G and Luri+ 2018A&A...616A...9L). Note (3): Flag as follows: g = Leid 33062 belongs to {omega} Cen. For this cluster, I assume the same as McDonald+ (2011MNRAS.417...20M); namely, the distance is 5kpc, and E(B-V)=0.12. A_V_=3.1*R_V_ is assumed (Mathis 1990ARA&A..28...37M). h = For NGC 104 (47 Tuc), I assume the same as McDonald+ (2011, J/ApJS/193/23); namely, the distance is 4.6kpc, and E(B-V)=0.04. A_V_=3.1*R_V_ is assumed (Mathis 1990ARA&A..28...37M). i = For NGC 5927, I assume 7.8kpc and E(B-V)=0.46 (Sloan+ 2010ApJ...719.1274S) and Av=3.1*E(B-V) (Mathis 1990ARA&A..28...37M). j = For NGC 6352, I assume 5.9kpc and E(B-V)=0.21 (Sloan+ 2010ApJ...719.1274S) and Av=3.1*E(B-V) (Mathis 1990ARA&A..28...37M). Note (4): Determined (unless otherwise indicated) from Drimmel+ (2003A&A...409..205D), assuming the distance, Dist. Note (5): Scalars applied to raw reduced Spitzer-IRS spectra from individual modules, with the entries in the following order: Short-Low/Long-Low/Short-High/Long-High (DL Cha is a special case, where the Spitzer-IRS spectrum was appended to the ISO-SWS spectrum (AOT 62804032) at the shortest wavelength of its Spitzer-IRS Short-High spectrum). Note (6): Mass weights equal to mass divided by the square of Earth-target distance and its uncertainty for all dust species at the temperature specified in the "Temp" column. One dust model is completely specified by two adjacent rows (with the same AOR). Note (7): The "Bayerite 1273K" and "Boehmite 1173K" are included in quotes because the samples no longer contain bayerite or boehmite, respectively, as noted in Section 3 of the text, but were obtained by heating these minerals at these temperatures. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Oct-2019