1,5,- 1Johns Hopkins University Applied Physics Laboratory, SES/SRE, Bldg 200 - E206, SES/SRE, Laurel, United States of America (carey.lisse@jhuapl.edu)
- 2Space Science Institute, Boulder, CO 80301, USA (sitko@SpaceScience.org)
- 3Chandra X-ray Center, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA (swolk@cfa.harvard.edu)
- 4Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, NE83-569, Cambridge, MA 02139, USA (hgunther@mit.edu)
- 5Department of Physics & Astronomy, 118 Kinard Laboratory, Clemson, SC 29634, USA (sbritt@clemson.edu)
- 6Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA (jgreen@stsci.edu)
- 7Planetary Science Institute, Tucson, AZ 85719, USA (jordan@psi.edu)
- 8Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA 10
- 9Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA (bcjohnson@purdue.edu)
- 10Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland (mariakout@cp.dias.ie)
- 11Department of Astronomy, Boston University, Boston, MA 02215, USA (cce@bu.edu)
- 12Department of Physics, Astronomy, & Geosciences, Towson State University, Towson, MD 21252, USA (alanjackson@towson.edu)
The Earliest Solar System Materials and Solar System Formation. Sun-like TTauri stars (TTS) grow in their final stages via magnetically focused mass flows from a circumstellar accretion disk (CAD) [1-2; Fig.1]. The CAD is also the site of formation of the first planetesimals, from asteroids to KBOs, but the processes by which CAD dust particles grow into planetesimals is not well understood. Some planetesimals may form through slow collisional aggregation of dust particles, while others form quickly through stochastic gravitational instabilities in dense regions of the CAD. Processing of CAD dust at high-temperatures, like the 1250-1650K temperatures of the CAD inner disk wall [3], is also required [4-5] to form the oldest known solid constituents of these planetesimals, refractory inclusions (RIs) and chondrules. The formation mechanisms for these oldest solid constituents are hotly debated, with model mechanisms ranging from stellar flare events to shock heating to CAD lightning to giant impacts [6-10].
Figure 1 – Infant T Tauri star schematic. Accretion occurs from an ~0.1Msun (CAD), driven by ionized material at the inner CAD wall focused by magnetic fields onto the protostar surface [1-2]. Outflow jets are sourced near the inner CAD wall. The inner wall, at T >1000K, occurs where the Keplerian period of orbiting CAD material matches the protostar’s rotation period.
Spectral Evidence that RWAurA harbors abundant amounts of chondrules and CAI-like material. The TTS system RWAurA (K1Ve, d=165 pc, 1.4Msun,~3Myr) is known to host an extended, active CAD [11-18]. Spitzer/IRS observations taken during the system’s quiescent phase ([19]; Fig. 2a) show the CAD’s 0.7–35 um spectrum can be described as the sum of a protostellar photosphere at ~4000K, the inner accretion disk wall at T~1300K, a CAD gap at ~2 au with apparent temperature Tgap~190K, and a very faint, cold (T~40K) component most likely due to the outer CAD envelope.
Figure 2 – (a) Combined 0.7-35 um RWAurA “quiescent” SED formed from 2006-2007 IRTF/SpeX 0.8–5.2 um spectra of (aqua,blue; [18]) plus a 2005 Spitzer/IRS spectrum [19] (black). Also shown are modified blackbody fits to the underlying continua from the protostellar surface (4000K), the inner CAD wall (1300K), a CAD gap (190K), and the CAD envelope sensed by ALMA (~40K; [16]). Assuming Twall ~217K/r[AU]0.57 [21] then Tinner wall=1300K at 0.06 AU and a Tgap =190K gap located at ~1.7AU from the primary.
(b) Spectral-compositional fit to the hot inner CAD wall emissivity of (a), showing evidence for impact silica, SiO gas, alumina, crystalline olivines, crystalline pyroxenes, phyllosilicates, and amorphous carbon. None of the low temperature amorphous silicates and magnesium sulfides typically seen in unprocessed ISM and cometary dust SEDs [22-24] are present, having been replaced by materials consistent with rapid high temperature processing of rocky materials (c.f. [25] & references therein).
Emission features due to a combination of ferromagnesian silicate and alumina/silica materials at 8–11 and 17–25 um as well as alumina at 12–14 um are seen from the hot (T~1300 K) inner system dust (Fig.2b). This compositional mineralogy is lacking in the amorphous silicates and metal sulfides found in molecular clouds and protosolar nebulae; instead it is rich in alteration products like high temperature glassy silicas, alumina oxides, crystalline silicates, and phyllosilicates[3, 20]. This dust has been heavily processed and altered to produce products akin to RIs and chondrules, and new higher resolution JWST spectra verify these findings.
A Dynamic, Rapidly Evolving System. RWAurA is a uniquely special laboratory to study RI and chondrule formation because recent work [3, 26-27] has demonstrated that energetic planetesimal collisions in the hot inner disk wall region have occurred there within the last decade. A tremendous drop in RWAurA’s normal visible (Fig. 3) and soft XUV emission was reported in 2014–2017, due to a “huge increase in a neutral extinctor” in the protostar’s atmosphere [26-27]. Coupled with an concomitant large increase in Fe K-shell X-rays [26-27], this suggests that huge amounts of obscuring gaseous iron (Fe) and fine “neutral” refractory rocky dust able to withstand prolonged temperatures > 1600K (= RIs) was created around the central protostar.
Figure 3 – (a) Optical lightcurve of RW Aur A for 2005–2025, showing relatively stable behavior from 2005 – 2010, a strong, short dip in 2011, more stable behavior in 2012–2014, a large unusual event/stochastic upset 2014-2020, and the onset of a new event in early 2025.
Our near-infrared (NIR) imaging and spectral monitoring observations of RWAurA [3, 28] over the last decade have shown evidence for a highly excited system with a bright, hot, asymmetric CAD, numerous hot atomic emission lines from the protostar’s atmosphere, and a new stochastic emission event in its high-speed focused outflow jets moving away at 100 – 200 km/s (Fig. 4). The hot (T~20,000K) bifurcated RWAurA jet spectral signature was seen to decay back to its normal pre-event level over the course of ~7 years, suggesting that Vesta-sized amounts of excess hot Fe+S+C+Si, common planetesimal core materials, had just blown out of the system’s jets. Conspicuously absent in the RWAurA jet spectral signatures were traces of any lithophilic elements that
Figure 4 – IRTF/SpeX 0.7–5.0 µm spectroscopic monitoring from 2006 to 2020 found a huge increase, circa 2018, in line emissions like the FeII 1.2557um line shown here, bifurcated by huge new jet outflows. By late 2020 the jets had subsided and the lines had returned to near-normal [3].
occur in the rocky mantles of differentiated planetesimals. These species remained in the solid phase, producing the “large amounts of reported new “neutral extinctors” in the protostar’s atmosphere [26-27]. Thus it is likely that the observed 2015 dimming event involved the catastrophic disruption of a primitive planetesimal, with easily vaporized Fe delivered into the jets and onto the protostar in the gas phase, while more refractory rocky materials melted and recondensed into highly refractory solid state materials like RIs and Chondrules.
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How to cite: Lisse, C., Sitko, M., Wolk, S., Günther, H.-M., Brittain, S., Green, J., Steckloff, J., Johnson, B., Koutoulaki, M., Espaillat, C., and Jackson, A.: Evidence for Ongoing Core Expulsion & Refractory Inclusion/Chondrule Formation in the RW Aurigae T-Tauri System , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-448, https://doi.org/10.5194/epsc-dps2025-448, 2025.
