EMISSION FROM WATER VAPOR AND ABSORPTION FROM OTHER GASES AT 5-7.5 μm INSPITZER-IRS SPECTRA OF PROTOPLANETARY DISKS

Abstract

In memory of Paola D'Alessio, who is dearly missed. ABSTRACTWe present spectra of 13 T Tauri stars in the Taurus-Auriga star-forming region showing emission in Spitzer Space Telescope Infrared Spectrograph (IRS) 5-7.5µm spectra from water vapor and absorption from other gases in these stars' protoplanetary disks. Seven stars' spectra show an emission feature at 6.6µm due to the ν 2 = 1-0 bending mode of water vapor, with the shape of the spectrum suggesting water vapor temperatures >500 K, though some of these spectra also show indications of an absorption band, likely from another molecule. This water vapor emission contrasts with the absorption from warm water vapor seen in the spectrum of the FU Orionis star V1057 Cyg. The other six of the thirteen stars have spectra showing a strong absorption band, peaking in strength at 5.6-5.7µm, which for some is consistent with gaseous formaldehyde (H 2 CO) and for others is

The chemistry of disks around T Tauri and Herbig Ae/Be stars

“…In the last years, near-IR to sub-mm observations have provided important constraints on the presence of water and its related radical (OH) in protoplanetary disks. At near- and mid-IR wavelengths, the spectra of disks around T Tauri stars show emission of hot H 2 O and OH arising from the inner disk (< a few au) atmosphere (Carr et al 2004; Carr & Najita 2008, 2011, 2014; Salyk et al 2008, 2011; Pontoppidan et al 2010a,b; Mandell et al 2012; Sargent et al 2014; Banzatti et al 2017), while in disks around Herbig Ae/Be stars, emission by OH is relatively common but there is a striking lack of H 2 O emission (Mandell et al 2008; Pontoppidan et al 2010a; Fedele et al 2011; Salyk et al 2011; Banzatti et al 2017). Far-IR observations with Herschel/PACS have essentially confirmed that the water detection rate is much higher in T Tauri disks than in disks around Herbig Ae/Be stars (Riviere-Marichalar et al 2012; Meeus et al 2012; Fedele et al 2012, 2013).…”

“… References: (1) Carr et al (2004); (2) Carr & Najita (2008); (3) Salyk et al (2008); (4) Pontoppidan et al (2010a); (5) Pontoppidan et al (2010b); (6) Carr & Najita (2011); (7) Salyk et al (2011); (8) Mandell et al (2012); (9) Riviere-Marichalar et al (2012); (10) Sargent et al (2014); (11) Banzatti et al (2017); (12) Fedele et al (2011); (13) Meeus et al (2012); (14) Fedele et al (2012); (15) Fedele et al (2013); (16) Hogerheijde et al (2011); (17) Podio et al (2013); (18) Du et al (2017); (19) van Dishoeck et al (2014); (20) Carr & Najita (2014); (21) Mandell et al (2008); (22) Lahuis et al (2006); (23) Gibb et al (2007); (24) Bast et al (2013); (25) Gibb & Horne (2013); (26) Kruger et al (2011); (27) Dutrey et al (1997); (28) Thi et al (2004); (29) Öberg et al (2010); (30) Öberg et al (2011); (31) Chapillon et al (2012a); (32) Kastner et al (2014); (33) Guilloteau et al (2016); (34) Fuente et al (2010); (35) Fuente et al (2012); (36) Graninger et al (2015); (37) Henning et al (2010); (38) Bergin et al (2016); (39) Schreyer et al (2008); (40) Pacheco-Vázquez et al (2015); (41) Aikawa et al (2003); (42) Pacheco-Vázquez et al (2016); (43) Loomis et al (2015); (44) Öberg et al (2017); (45) Qi et al (2013a); (46) Carney et al (2017); (47) Walsh et al (2016); (48) Chapillon et al (2012b); (49) Öberg et al (2015); (50) Qi et al (2013b); (51) Salinas et al (2016); (52) Dutrey et al (2011); (53) Qi et al (2003); (54) Dutrey et al (2007); (55) Teague et al (2015); (56) Mathews et al (2013); (57) Qi et al (2013c); (58) Thi et al (2011). Notes: a Values are line intensity ratios rather than abundance ratios. b Out of this range, …”

“…For example, thanks to ALMA it has been possible to detect new molecules such as cyclic C 3 H 2 (Qi et al 2013b; Bergin et al 2016), CH 3 CN (Öberg et al 2015), and CH 3 OH (Walsh et al 2016), and to image the CO snowline in a few disks (Mathews et al 2013; Qi et al 2013c, 2015; Schwarz et al 2016; Zhang et al 2017). Infrared (IR) observations using space telescopes such as Spitzer and ground-based facilities such as the Very Large Telescope (VLT) and the Keck Observatory telescopes have provided a view of the molecular content of the very inner regions of protoplanetary disks, where absorption and emission lines from molecules such as CO, CO 2 , H 2 O, OH, HCN, C 2 H 2 , and CH 4 have been routinely observed (Lahuis et al 2006; Gibb et al 2007; Salyk et al 2007, 2008, 2011; Carr & Najita 2008, 2011, 2014; Pontoppidan et al 2010a,b; Najita et al 2010, 2013; Kruger et al 2011; Doppmann et al 2011; Fedele et al 2011; Mandell et al 2012; Bast et al 2013; Gibb & Horne 2013; Sargent et al 2014; Banzatti et al 2017). The launch of the Herschel Space Observatory was also very helpful to investigate the chemical content at far-IR wavelengths, with the detection of molecules such as CH + (Thi et al 2011) and NH 3 (Salinas et al 2016), and the exhaustive characterization of H 2 O and OH from the inner to the outer regions (Hogerheijde et al 2011; Riviere-Marichalar et al 2012; Meeus et al 2012; Fedele et al 2012, 2013; Podio et al 2013).…”

The Infrared Evolution of Dust in V838 Monocerotis

“…Figure 3 shows the continuum subtracted residual emission, highlighting potential emission features. Features near 6.30 µm and 6.85 µm have been associated with water vapor emission (ν 2 bands) and formaldehyde (H 2 CO) in spectra of the dense circumstellar disk environments of T Tauri stars (Sargent et al 2014). Higher spectral resolution observations with instruments like EXES (Richter et al 2018) on SOFIA or MIRI on the James Webb Space Telescope (JWST) are necessary to confirm these identifications.…”

Infrared Spectroscopic Studies of Gases in the Circumstellar Environments of Young Stellar Objects

“…Though many previous studies found evidence for water from Spitzer-IRS high resolution (R ∼ 600) spectra (e.g., Carr & Najita 2008), we find that Spitzer-IRS low resolution (R ∼ 90) spectra can identify water emission as well (note Pascucci et al 2009 andTeske et al 2011 identified HCN and C 2 H 2 in Spitzer-IRS low resolution spectra). Models of low resolution Spitzer-IRS spectra of protoplanetary disks around young stars suggest the presence of H 2 O, H 2 CO, and HCOOH in these protoplanetary disks (Sargent et al 2014). We are seeking high resolution infrared spectroscopic confirmation of the presence of these molecules (e.g., Roueff et al 2006 found absorption at 3.6 µm in the spectrum of protostar W33A from H 2 CO).…”