JET-TORUS INTERACTIONS IN BIPOLAR PRE-PLANETARY NEBULAE
Applicant: Po-Sheng Huang (Ph.D. student) Institute of Astrophysics, National Taiwan University
Thesis Adviser: Dr. Chin-Fei Lee
Institute of Astronomy and Astrophysics, Academia Sinica
Abstract
It is still an enigma of how spherical envelopes of asymptotic giant branch (AGB) stars evolve to aspherical planetary nebulae (PNs). Recent studies suggest that evolved stars could drive collimated fast winds (CFWs) or collimated jets in the end of the AGB phase, interacting with the slowly expanding AGB envelopes and tori. The interactions dramatically change the morphology of circumstellar envelopes (CSEs), forming bipolar pre-planetary nebulae (PPNs), as a kind of transient objects in between the AGB phase and the PN phase. This shaping mechanism has been checked by observing many bipolar PPNs in optical, infrared (IR), and radio wavelengths, and tested by hydrodynamical simulations. Nevertheless, the underlying jets are still mostly undetected due to a lack of observations with sufficient angular resolution and sensitivity. Now with the Atacama Large Millimeter/submillimeter Array (ALMA), which has unprecedented high resolution and sensitivity, we expect to detect the jets. Thus, we propose for ALMA observations to search for the jets again and to confirm the jet interactions, in col- laboration with a well-established scientist Dr. Raghvendra Sahai in Jet Propulsion Laboratory (JPL). Dr. Sahai has been a long-term collaborator of my thesis adviser Dr. Chin-Fei Lee.
His extensive experience in multi-wavelength observations will provide different insights for jet searching and for studying the morphology and kinematics of PPNs. We will also continue sim- ulations of jet-torus interactions. Previous observations have provided us physical parameters for the jet-torus interaction, such as mass-loss rates, momentum fluxes, etc. We will compare our simulations with the observations (including previous observations and new observations to be obtained with ALMA) in order to confirm the jet interactions and derive the jet properties.
Our final goal is to solve the long-standing problem of how a spherical envelope evolves to a bipolar PPN and PN.
1 Recent Publications
My research is focused on the mass-loss of AGB/post-AGB stars and PPNs, especially on jets and bullets, and their interactions with AGB/post-AGB winds. My research methods include 3D hy- drodynamical simulations, SMA and ALMA data analysis based on the softwares of MIR/Miriad and CASA, and radiative transfer modeling of molecular outflows and CSEs. Follows are my recent publications.
• First-author paper:
– “The Shaping of the Multipolar Pre-Planetary Nebula CRL 618 by Multidirectional Bullets00, Huang, P.-S., Lee, C.-F., Moraghan, A., & Smith, Michael. 2016, ApJ, 820, 134.
– One paper (Huang et al., in prep.) will be published in this year (see, $2.3 Research Methods).
• Non-first-author papers:
– “Multiple Fast Molecular Outflows in the Pre-planetary Nebula CRL 61800, Lee, C.-F., Sahai, R., Snchez Contreras, C., Huang, P.-S., & Hao Tay, J. J. 2013, ApJ, 777, 37.
– “A study of the wiggle morphology of HH 211 through numerical simulations00, Moraghan, A., Lee, C.-F., Huang, P.-S., & Vaidya, B. 2016, MNRAS, 460, 1829M.
In addition, we have proposed SMA and ALMA observations in order to study bipolar PPNs.
In this year, at least one additional paper of previous SMA observational result will be published.
These works successfully show the shaping process of PPN lobes and the mass-loss properties. In the future, we plan to use ALMA to obtain more precise observations of jets and tori. We expect more understanding to the jets and the nature of PPNs and PNs.
2 Research Plan
2.1 Scientific Background
Stellar evolution in the late stage of stars is always a popular topic in astronomy and astrophysics.
Typical low- to intermediate-mass stars, such as our sun, will evolve off the main sequence and go through the red-giant branch, horizontal branch and asymptotic giant branch (AGB). Afterwards, these stars will use an extremely gorgeous way to declare their death – transform to PNs with beautiful and complex structures. In the observations, most of PNs have elliptical or bipolar structures, but the shaping mechanism is still unclear. In order to understand how spherical envelopes of stars transform to aspherical or even bipolar PNs, people focus on studying PPNs – the transient objects between the AGB phase and the PN phase. In addition, most of the PPNs already developed bipolar or multipolar lobes, which means that the shaping process must have started early in the PPN phase.
A bipolar PPN usually consists of a fast extending bipolar lobe and a toroidal envelope (or simply torus) surrounding the central star and an outer shell of spherical AGB halo. Several mechanisms have been proposed in order to explain the shaping process of bipolar PPNs. Some hypotheses include a binary system, which consists a white dwarf (WD) or main sequence star and a post-AGB star.
An accretion disk is formed around the WD or the main sequence star when the material is accreted from the post-AGB star (e.g., Morris 1987), and then a bipolar jet or CFW is launched perpendicular to the disk (Frank & Blackman 2004). Sahai & Trauger (1998) proposed that CFWs or jets ejected in the late AGB phase are the primary agent for shaping the complex structures of PPNs and PNs.
The jets colliding with slowly expanding AGB/post-AGB winds around the central stars extremely change the morphology of the envelopes, forming bipolar lobes. This shaping mechanism has been checked by observing many bipolar PPNs in optical, infrared (IR), and radio wavelengths, and tested by hydrodynamical simulations. Nevertheless, the underlying jets are still mostly undetected due to a lack of observations with sufficient angular resolution and sensitivity. Now with the Atacama Large Millimeter/submillimeter Array (ALMA), which has unprecedented high resolution and sensitivity, we expect to detect the jets.
2.2 Objective
Our research objective is to propose ALMA observations for jet hunting, in collaboration with Dr.
Raghvendra Sahai in JPL. Dr. Sahai has been a long-term collaborator of my thesis adviser Dr.
Lee. His extensive experience in multi-wavelength observations will provide different insights for jet searching and for studying the morphology and kinematics of PPNs. We will also continue simulations of jet-torus interactions. Previous observations have provided us physical parameters for the jet-torus interaction, such as mass-loss rates, momentum fluxes, etc. We will compare our simulations with
the observations (including previous observations and new observations to be obtained with ALMA) in order to confirm the jet interactions and derive the jet properties. Our final goal is to solve the long-standing problem of how a spherical envelope evolves to a bipolar PPN and PN.
2.3 Research Methods
In order to precisely describe jet properties in our ALMA proposal, we have studied jet interactions with tori in the previous observations. The jet-torus interactions produce shocks, which can be traced by molecular outflows or optical shells. For example, the outflows show the mass-loss rates and momentum flux of the jets and tori. By studying the optical and near-IR images, and spectroscopies, we will obtain detailed structures and kinematics of the shells. According to these derived properties, we can use hydrodynamical simulations to confirm the jet-torus interactions. In the following, I introduce one of our targets and research methods as an example. It has been observed by using the SMA in high resolution. As a reference of our ALMA proposal, the result is prepared to be published in this year. We will also combine our results with Dr. Sahai’s previous works to confine our jet model, and then use 3D simulations to study the shaping process of bipolar PPNs.
2.3.1 Observations of IRAS 17150-3224
IRAS 17150-3224 (I17150) is a bipolar PPN at a distance of ∼3 kpc (Bujarrabal et al. 2001; Meixner et al. 2002) with a length of 600 extended in the northwest(NW)-southeast(SE) direction with a position angle (P.A.) of −40◦ in the HST optical image. Hu et al. (1993) have made extensive observations of this object in optical and (sub-)mm. The spectral energy distribution shows double peaks, suggesting that the dusty torus has been detached from the photosphere and the AGB wind has ended (Kwok et al. 1996). It has a torus with an expansion velocity of 12-15 km s−1 and a mass-loss rate of ∼ 5.3 × 10−4 M yr−1 (Bujarrabal et al. 2001; Meixner et al. 2002; Huang et al., in prep.). According to our SMA observation in CO J = 2–1, the kinematical ages of the torus and the outflow are ∼1800 yr and ∼1000 yr, respectively.
We have obtained the CO J = 2–1 maps of IRAS 17150–3224 by using the SMA, with a resolution of
∼100. 9 × 100. 1. In our study, we have used the high-velocity (HV) map Figure 1(a) to analyze the elongated structures along the optical lobes. The outflow axes (P.A. = −60◦) did not overlap with the axis of the optical lobe. In the SE, the offset between the HV redshift emission peak and the lobe axis is ∼000. 5. In the NW, the front shell and the backward shell of the outflow have different peaks in two sides along the lobe axis. In Figure 1(b), we use a channel map in the systemic velocity of I17150 to show the torus. The toroidal envelope is not perpendicular to the outflow axis. The reason is unclear because the torus is not fully resolved.
Figure 1(a) and (b) imply a model consists of a bipolar jet and a torus. Therefore, we construct a simple model as shown in Figure 2. In order to obtain the physical properties of I17150, we also use radiative transfer to calculate the CO emission of the outflow and torus in our model. The results are shown in Figure 3. The radiative transfer is calculated from the gas density, temperature, and kinematics of our PPN model, which consists of a torus and a bipolar outflow. Currently, we derive a torus mass of ∼1.09 M and the outflow mass of ∼0.93 M . More results will be published in this year.
2.3.2 ZEUS-3D Simulations
ZEUS-3D is a grid-based computational fluid dynamics code (Clarke 1996, 2010). The code has been expanded to include molecular and atomic cooling by Suttner et al. (1997). In addition, molecular chemistry is also included in order to calculate the fraction of molecular hydrogen and atomic hydrogen (Smith & Rosen 2003). We have used the ZEUS-3D simulation to study the shaping process of multiple lobes of a PPN CRL 618 (Huang et al. 2016). For example, our simulations can reproduce the morphology of the multipolar lobes of CRL 618 (Fig. 4). The simulated CO emissions by using the radiative transfer show the structure and the
Figure 1: Panel (a) shows the HV map overlaid on the optical image of I17150. The blue contours (from −7.1 to 0.3 km s−1) and the red contours (from 24.6 to 35.1 km s−1) trace the bipolar outflow along the optical lobes. Also notice that the integrated velocity ranges of the blue wing and the red wing are different. The blue wing is faster than the red wing (∼23 km s−1 to ∼19 km s−1). The contour level shows that the emission of the NW outflow is stronger than that of the SE outflow. The red contours can be separated in two sides, implying that the two components tracing the bipolar outflow in opposite directions. The red contour in the NW near the center should trace the shock shell behind the blueshift emission. In the same manner, the blue contour in the SE near the center should trace the shock shell in front of the redshift emission. Panel (b) shows the CO J = 2–1 emission of systemic velocity channel at ∼16 km s−1. This map shows the torus-like structure near the central star.
Figure 2: Velocity distribution in a simple model of I17150. Based on the optical and the SMA observation, we assume two components in our model: an expanding torus in the waist and a bipolar outflow. The center of the torus has a hole excavated by the bipolar outflow. In our observation, a beam size of ∼100. 9 × 100. 1 can not totally resolve the outflow. Therefore, its structure is not fully understood. Here we assume that the outflow consists of two shells bounded by an outer ellipsoid and an inner ellipsoid with a radius ∼3000 AU.
Figure 3: Panel (a) and (b) show the high-velocity (HV) map and the systemic velocity (vsys) map calculated from our radiative transfer model for I17150, respectively. The bipolar outflow and toroidal emission shows similar structures compared to the observation (Fig. 1).
Figure 4: The ZEUS-3D hydrodynamical simulation for a multipolar PPN CRL 618 (Huang et al.
2016). The color shows the column density at 90 yr. Five bullets are ejected in two episodes, producing the five eastern lobes of CRL 618. In the first episode, two bullets are ejected, producing lobes E1 and E2. In the second episode (∼ 40 yr after the first episode), three bullets are ejected, producing lobes E3, E4, and E5. A U-shaped cavity wall is seen at the base, consisting of swept-up material in the dense core.
kinematics of the molecular outflows similar to those seen in the observations. Furthermore, the total mass of the bullets is consistent with the observed high-velocity CO emission in fast molecular outflows. Since the simulation has reproduced the observational results reasonably well, we will also use ZEUS-3D simulation to study the shaping process and the initial condition of bipolar jet and torus in I17150 and I22036.
3 Plan Adviser Dr. Sahai (JPL)
It was my pressure to first meet Dr. Raghvendra Sahai in the 11th Pacific Rim Conference on Stellar Astrophysics (PRCSA) in Hong Kong last year. The 11th PRCSA is dedicated to Prof. Sun Kwok because his contribution has innovated our understanding of PPNs and PNs. Dr. Sahai is also one of the greatest scientists in Astronomy. Dr. Lee introduced me to Dr. Sahai and let me have a good opportunity to present our recent simulational results to him and other participants. I learned a lot from him during this conference and I’d like to cooperate with him for my current research. Therefore, I propose this study program to him and he agreed with that immediately.
Following is a brief introduction to Dr. Sahai. Dr. Sahai’s research has focused on the mass-loss in AGB/post-AGB stars, PPNs and PNs, in the observations of optical, infrared, and radio wavelengths. He has published over 80 papers in these areas. Dr. Sahai is focusing on the research of using NASA’s Great Observatories (Hubble Space T elescope [HST ], Chandra X-Ray Observatory and Spitzer Space Telescope) to study evolved stars. He has contributed to the science justification for an infrared high-contrast coro- nagraphic imaging camera to search for planetary and brown dwarf companions around nearby stars, and circumstellar matter in young, main-sequence and dying stars, as part of the Design Reference Mission for the JWST. He is a member of the Science Team for the ECLIPSE coronagraphic telescope concept for a
DISCOVERY-class mission to search for extra-solar giant planets. He is a full member of the American Astronomical Society and the International Astronomical Union, and a founding member of the European Astronomical Society.
Dr. Sahai and my thesis adviser Dr. Lee have collaborated for a long time. There are two papers about the PPN CRL 618 in collaboration with Dr. Sahai:
1. “Shaping Proto-Planetary and Young Planetary Nebulae with Collimated Fast Winds00, Lee, C.-F., &
Sahai, R. 2003, ApJ, 586, 319.
2. “Collimated Fast Wind in the Preplanetary Nebula CRL 61800, Lee, C.-F., Hsu, M.-C., & Sahai, R.
2009, ApJ, 696, 1630.
3. “Mapping the Central Region of the PPN CRL 618 at Sub-arcsecond Resolution at 350 GHz00, Lee, C.-F., Yang, C.-H., Sahai, R., & Sanchez Contreras, C. 2013a, ApJ, 770, 153.
4. “Multiple Fast Molecular Outflows in the Pre-planetary Nebula CRL 61800, Lee, C.-F., Sahai, R., Snchez Contreras, C., Huang, P.-S., & Hao Tay, J. J. 2013b, ApJ, 777, 37.
In the following, I list a part of Dr. Sahai’s publications of PPNs.
1. “The Starfish Twins: Two Young Planetary Nebulae with Extreme Multipolar Morphology00, Sahai, R. 2000, ApJ, 537, L43.
2. “X-Ray Emission from the Preplanetary Nebula He3-147500, Sahai, R., Kastner, J.H., Morris, M., Frank, A., Blackman, E.G. 2003, ApJ, 599, L87.
3. “A Massive Bipolar Outflow and a Dusty Torus with Large Grains in the Pre-Planetary Nebula IRAS 22036+530600, Sahai, R., Young, K., Patel, N.A., Snchez Contreras, C. and Morris, M. 2006, ApJ, 653, 1241.
4. “Preplanetary Nebulae: An HST Imaging Survey and a New Morphological Classification System00, Sahai, R., Morris, M., Snchez Contreras, C., & Claussen, M. 2007, AJ, 134, 2200.
5. “Sculpting a Pre-planetary Nebula with a Precessing Jet: IRAS 16342-381400, Sahai, R.; Le Mignant, D., Snchez Contreras, C., Campbell, R. D., Chaffee, F. H. 2005, ApJ, 622, L53.
6. “Young Planetary Nebulae: Hubble Space Telescope Imaging and a New Morphological Classification System00, Sahai, R., Morris, M. R., & Villar, G. G. 2011, AJ, 141, 134.
7. “ALMA Observations of the Coldest Place in the Universe: The Boomerang Nebula00, Sahai, R., Vlemmings, W. H. T., Huggins, P. J., Nyman, L.-., & Gonidakis, I. 2013, ApJ, 777, 92.
8. Sahai, R. 2013, “From AGB Stars to Aspherical Planetary Nebulae An Observational Per-spective00, invited review, in Asymmetric Planetary Nebulae VI, conference held Nov. 48, 2013, Riviera Maya, Mexico.
4 Expected Results
Our studies of the jet-torus interactions will help to understand the shaping of bipolar lobes and the nature of the jets and tori, and also benefit to propose new ALMA observations to resolve the jets near the central stars. We expect to obtain the new ALMA observing time for bipolar PPNs and publish papers in the following years. In addition, the new simulations for the jet model will be published in the next year. This study program is very important not only in the research of PPN jets, but also provide a new opportunity to our future collaborations with people in JPL, especially for young astrophysicists in Taiwan.
5 References
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Clarke, D. A. 2010, ApJS, 187, 119
Frank, A., & Blackman, E. G. 2004, ApJ, 614, 737 Hu, J. Y. et al. 1993, A&A, 273, 185
Huang, P.-S. et al. 2016, ApJ, 820, 134 Huggins, P. J. 2007, ApJ, 663, 342
Lee, C.-F., & Sahai, R. 2003, ApJ, 586, 319
Lee, C.-F., Hsu, M.-C., & Sahai, R. 2009, ApJ, 696, 1630 Lee, C.-F. et al. 2013b, ApJ, 777, 37
Lee, C.-F. et al. 2013a, ApJ, 770, 153 Meixner, M. et al. 2002, ApJ, 571, 936
Moraghan, A. et al. 2016, MNRAS, 460, 1829M Morris, M. 1987, PASP, 99, 1115
Sahai, R. & Trauger, J. T. 1998, AJ, 116, 1357 Sahai, R. et al. 2003, ApJ, 586, L81
Sahai, R. et al. 2006, ApJ, 653, 1241
Smith, M. D., & Rosen, A. 2003, MNRAS, 339, 133 Suttner, G. et al. 1997, A&A, 318, 595
Ostriker, E. C. et al. 2001, ApJ, 557, 443 Vel´azquez, P. F. et al. 2014, ApJ, 794, 128 Woods, P. M. et al. 2005, A&A, 429, 977
