Class Time: W 10:10 - 11:00 Class Room: 538 Davey Lab
Professor: Robin Ciardullo Office: 519 Davey Lab
Office Hours: MF 3:30-4:30 or any other time Zoom Address: https://psu.zoom.us/j/3404085003
e-mail: rbc@astro.psu.edu Web page: https://sites.google.com/psu.edu/robin-ciardullo/teaching/astro-589-seminar
Planetary Nebulae are like the Swiss Army Knives of extragalactic astronomy and cosmology. They are never the obvious tool to attack a problem, but often times they provide unique insight into a phenomenon, yielding data that may, or may not, be consistent with conventional analyses.
Unlike some seminars that delve deeply into a single topic, this seminar will touch on a host of important problems in astrophysics and consider how planetary nebulae can help answer them. The topics covered will include the frequency of binary stars (and Jupiter-like planets) in the Milky Way PNe, the formation history of the disk galaxies, the missing satellites problem, the chemical evolution of galaxies, the dark matter distributions of elliptical galaxies, and the problem of "tension" in the Hubble Constant.
The topics are listed below, along with papers that represent good starting points. The discussion of each topic will be lead by 3 students. To use the parlance frequently used in NASA and NSF panels, each topic will have 3 reviewers: a Primary reviewer, who has overall responsibility for presenting the material and leading the scientific discussion, and two Secondary reviewers, who will assist the Primary and present their own takes on the problem. (Unlike the NASA and NSF panels, the 3 reviews need not be independent -- the reviewers can and should coordinate their work.) But all students should be familiar with the topic under consideration (i.e., they should have least skimmed the week's papers) and participate in the discussion. A successful discussion will
1) Present the background on the subject (i.e., what is the problem and what is known from other methods/techniques),
2) Describe how PNe can be used to help address the problem (i.e., it's advantages and drawbacks),
3) Give the current results from the PNe, and (perhaps most importantly),
4) Discuss what new observations/analyses should be done to push the field forward.
Grades will be based on the quality of the presentations/discussion and class participation.
A table containing the names of the 3 reviewers for each topic is given at the bottom of this page. Note that the last 2 weeks are still TBD, so we have time to expand some discussion over two weeks, or add new topics.
Outline of the Topics
Week 1: Review of Stellar Evolution and Planetary Nebulae
[No seminar topic]
Week 2: Planetary Nebulae and non-PN Post-AGB Stars
The Problem: The timescale for post-AGB evolution depends on the mass of the star: the lower the mass, the less luminous the object, and the longer the evolutionary time. If the mass is low enough, the mass lost during the AGB phase will disperse long before the star is hot enough to ionize the material. Where is this luminosity limit? Should there also be a lower limit to the naked PAGB luminosities due to the age of the universe? Or does the second parameter problem doom us? Could post-AGB stars be used as precision standard candles in Population II systems? Can post-AGB stars in Population I systems teach us anything?
Starting Points: Bond 1977, IAU Symp 180, p. 460 ; Ciardullo et al. 2022, ApJ 930, 145 ; Oudmaijer et al. MNRAS 516, L61
Week 3: Planetary nebulae and binary stars (+ large planets)
The Problem: Most planetary nebulae are not spherically symmetric. So what shapes them? The most obvious mechanism is the injection of angular momentum into the nebula by an orbiting object, such as a companion star or a planet. Does this mean that most PNe are formed from binary stars? Can large planets shape the nebula? What does theory have to say? What do the observations have to say?
Starting Point: Boffin & Jones 2019, The Importance of Binaries in the Formation and Evolution of Planetary Nebulae
Week 4: The Luminosities and Temperatures of Planetary Nebula Central Stars
The Problem: There are thousands of PNe known in the Milky Way. But a very small number of PNe have accurate distances: many distance uncertainties are a factor of 2, and factor of 10 errors are not unknown. (Gaia is changing this, but measuring a star in the bright background of a nebula is not what Gaia was designed for.) What is the status of placing PN central stars on the HR diagram and comparing to evolutionary tracks? How do observations compare to predictions of post-asymptotic giant branch evolutionary models? What do they teach us about AGB mass loss?
Starting Points: González-Santamaría et al. 2021, A&A, 656, 51 ; Miller Bertolami 2016, A&A 588, A25
Week 5: Planetary Nebulae in Star Clusters
The Problem: The population of planetary nebulae is quite diverse, and it is difficult to know for certain the masses and metallicities of their progenitor stars. The exception is when a planetary nebula is discovered within a star cluster: for those objects, one can compare the properties of the PN to that of stars at the cluster's main-sequence turnoff. How many such objects are there? What do they tell us about stellar evolution and stellar mass loss? Are the results consistent with models?
Starting Points: Fragkou et al. 2022, ApJ Letters, 935, L35 ; Jacoby et al. 2017, ApJ 836, 93
Week 6: The Bright-end Cutoff of the [O III] λ5007 Planetary Nebula Luminosity Function
The Problem: The absolute luminosity of the bright-end cutoff of a galaxy's [O III] λ5007 planetary nebula luminosity function (PNLF) appears to be remarkable independent of its age, metallicity, star-formation history. (The bright-end PNLF of elliptical galaxies is the same as that of spirals.) How can that be? How can elliptical galaxies produce the bright PNe that are observed?
Starting points: Marigo et al. 2004, A&A 423, 995 ; Ciardullo et al. 2005, ApJ 629, 499 ; Ciardullo 2012, Ap&SS 341, 151 ; Gesicki et al. 2018, Nature Astronomy, 2, 580 ; Ciardullo & Jacoby 1999, ApJ 515, 191 ; Davis et al. 2018, ApJ 863, 189 ; Valenzuela et al. 2019, ApJ 887, 65
Week 7: The [O III] λ5007 Planetary Nebula Luminosity Function and the Hubble Constant
The Problem: Currently, there is a 3 to 5-sigma tension between the Hubble Constant as measured via the distance ladder, and that measured from the microwave background and the assumption of a cosmological constant. Can the PNLF help address this tension? What issues stand in the way of doing this?
Starting Point: Ciardullo 2022, Frontiers in Astron & Spa. Sci, 9, 896326
Week 8: Planetary Nebulae and the UV Emission of Galaxies
The Problem: Elliptical galaxies consist mostly of red main sequence and red giant stars. Yet when you look at their spectra, many have a "UV upturn", i.e., instead of a monotonically decreasing amount of light in the blue, the spectrum of the galaxy turns up shortward of ~2000 Å. What is the source of this light. Is it extremely blue horizontal branch stars? Hot post-asymptotic giant branch stars? UV leakage from PN central stars? What does this tell us about the stellar population of elliptical galaxies?
Starting Point: Stasińska et al. 2022, Frontiers in Astron & Spa. Sci., 9, 3485 ; Buzzoni 2007, ASP Conf. Ser. 374, 311
Week 9: The Chemical Abundances of Planetary Nebulae
The Problem: The nebula of a PN displays bright optical emission lines of O, N, He, Ne, S, and Ar. What do we know about the abundances of these elements? How to do they compare to expectations? Is there evidence for processing of the elements during stellar evolution? What do the PNe tell us about the chemistry of the Milky Way?
Starting Point: Delgado-Inglada 2017, I.A.U. Symp. 323, 51 ; Kwitter & Henry 2022, Pub A.S.P. 134, 022001
Week 10: Planetary Nebulae and Galactic Chemical Evolution
The Problem: If one can determine the luminosities and temperatures of PN central stars, then one should be able to estimate the central star masses via a comparison to post-AGB evolutionary tracks. If one knows the PN's central star mass, then one should be able to estimate the initial mass of the star via the initial to final-mass relation. If one knows the star's initial mass, then one knows its age. Thus, in theory, one can compare the ages of an ensemble of PNe to their chemical abundances and track a system's chemical evolution. Is this really possible? Where are the problems and can we solve them?
Starting Points: Gonçalves 2019, in IAU Symp. 344, 161 ; Arnaboldi et al. 2022, A&A 666, A109
Week 11: Planetary Nebulae and the Structure of Spiral Disks
The Problem: The z-motions of stars in a spiral galaxy's disk are defined by the surface density of the disk and the scale height of the stars. Since PN in other galaxies are essentially monochromatic stars (emitting most of their light in [O III] λ5007), measuring their radial velocities is easy. So one can use PNe to measuring the mass (and mass-to-light ratio) of a galaxy's disk, for comparison to its dark matter mass. What are the results of such an analysis? What additional work should be pursued? Can this help us attack the missing satellite problem?
Starting Point: Herrmann & Ciardullo 2009, ApJ, 705, 1686 ; Herrmann et al. 2009, ApJ Letters, 693, L19 ; Bershady et al. 2010, ApJ 716, 198
Week 12: Planetary Nebulae and the Dark Matter of Elliptical Galaxies
The Problem: One of the most startling results of the early 1990's was the discovery of a seemingly normal elliptical galaxy with very little, if any dark matter. This spawned the creation of the Planetary Nebula Spectrograph, an instrument specifically designed to check this result. What are the results from the instrument? Are normal elliptical galaxies without dark matter still a thing? How can such an object be created?
Starting Point: Douglas et al. 2007, ApJ 664, 257 ; de Lorenzi et al. 2009, ApJ 395, 76 ; Pulsoni et al. 2018, A&A 618, A94
Week 13: Planetary Nebulae and the Formation of Galaxy Clusters
The Problem: When a dwarf galaxy falls into the Milky Way, it gets disrupted, leaving a stream of stars across the sky in leading and trailing orbits. The study of these stars is called Galactic Archaeology. The same thing happens when a galaxy falls into a galaxy cluster. Thus, it is possible to use PNe to study Galaxy Cluster Archaeology. What do we know about the intracluster stars? Can PNe help understand the formation and evolution of galaxy clusters? If so, how?
Starting point: Arnaboldi & Gerhard 2022, Frontiers in Astro & Spa. Sci, 9, 403
Week 14: Photometry and Spectroscopy of Extragalactic Planetary Nebulae
The Problem: While planetary nebulae in the Milky Way and Magellanic Cloud are usually resolved and can be quite bright, PNe in other galaxies are just faint point sources. Even in Local Group galaxies, it has been difficult to obtain spectra of large numbers of objects and learn about their systematics. But the era of big telescopes and integral-field-unit spectrographs is changing this.
Starting point: Roth et al. (2023), IAU Symposium 384
Week 15: Planetary Nebulae and the Cold Universe
The Problem: There's more to a planetary nebula than a hot central star surrounded by ionized gas. In many/most cases, not all the mass ejected from the progenitor star is ionized: PN are often surrounded by dust and a rich assorted of molecules and solid-state matter, both organic and inorganic. This diversity is important for not only important for constraining the chemical enrichment of the galaxy, but also understanding the properties of our own solar system.
Starting point: Kwok 2022, Frontiers in Astro & Spa. Sci., 9, 893061
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