1. STELLAR REMNANT PLANET INVENTORY Session 1.1 Neutron star planets - - PDF document

• 1. STELLAR REMNANT PLANET INVENTORY

Session 1.1 Neutron star planets

Monday, January 23 PSR B1257+12 planets: status and future prospects

Alex Wolszczan (Penn State University)

I will summarize the current observational status of the PSR B1257+12 planets, 20 years after the announcement of their discovery. I will also discuss issues related to neutron star planet detectability with the pulsar timing technique.

Where are the other pulsar-planet systems?

Scott Ransom (National Radio Astronomy Observatory)

It's been twenty years since the spectacular pulsar planetary system B1257+12 was announced. At the time, not even 20 millisecond pulsars had been timed consistently or precisely enough to be able to detect such systems. Since then, more than 150 millisecond pulsars have had precise timing solutions established, yet only a single additional pulsar- planet system has materialized: the very strange triple system B1620-26 in globular cluster M4. So where are the

• thers? The simple answer is: they aren't there. However, there is at least one potential "new" pulsar planetary

system around an "isolated" pulsar in the globular cluster NGC6440. Unfortunately, confirming that the anomalous timing behavior is really planets has been (so far) impossible. Over the next 5 years we expect the number of known millisecond pulsars to grow by almost a factor of two. Will we find more pulsar-planet systems? Or will B1257+12 continue to grow in its "exotic-ness"?

The Puzzle of the Planet around PSR1620-26

Steinn Sigurdsson (Penn State University)

I review the extraordinary exoplanet orbiting a binary pulsar in the globular cluster M4, including an update on the

• ngoing observing program and current status of the parameters of the system. I also briefly discuss the broader

implications of the system and the prospects for planet in globular clusters.

Transformation of a Star into a Planet in a Millisecond Pulsar Binary

Matthew Bailes (Swinburne University of Technology) and the HTRU team

We have discovered a very short orbital period pulsar binary that comprises of a millisecond pulsar and a Jupiter- mass planet. Roche Lobe considerations suggest that the density is >22 g/cc and that the star is the evolved core of the once-massive star that recycled the pulsar. Mass-radius relations suggest that this system may comprise of the core of a Carbon white dwarf that was once an ultra-compact low-mass X-ray binary and expanded until it reached its current mass at which time to spiral-out ceased leaving the system in its current configuration. Unlike the original Millisecond pulsar with planets, the transverse velocity of this system appears to be very low.

Substellar companions around young neutron stars

Bettina Posselt (Penn State University)

Young neutron stars show often timing noise at radio frequencies and some are radio-quiet. It is therefore difficult to search for planets around these neutron stars by radio timing. However, substellar companions around young neutron stars are expected to be still warm enough for substantial thermal emission in the Near-Infrared. Since the

neutron stars are very faint in the NIR, direct imaging can unobstructively detect co-moving, warm companions. We will present the current state of our direct imaging campaign to search for substellar companions around nearby, young neutron stars and give a short outlook regarding this search with future observing facilities.

Session 1.2 Subdwarf planets

Monday, January 23 SdB Planets

Roberto Silvotti (INAF - Osservatorio Astronomico di Torino) et al

In this talk I will make a short review on sdB planets, in particular from an observational point of view, and I will present/discuss recent results from space (Kepler) and from ground based photometry.

Small planets in tight orbits around a hot B subdwarf star

Stephane Charpinet (Institut de Recherche en Astrophysique et Planétologie)

We present the discovery, based on Kepler ultra-high precision photometry, of two small planet candidates orbiting very close to a hot B subdwarf star. This star is essentially the hot and compact He burning remnant of a former red- giant core left exposed by the loss of nearly all of the red-giant envelope. This discovery may then be the first documented case suggesting that planets can have a significant role in influencing the late stages of stellar evolution.

Substellar companion candidates around two pulsating sdB stars

Ronny Lutz (Institut für Astrophysik Göttingen)

One possible formation scenario to explain the existence of single subdwarf B stars includes the presence of

• substellarcompanions. We search for substellar companions around two pulsating single sdB stars, HS 0444+0458

(V1636 Ori) and HS 0702+6043 (DW Lyn) by means of a timing method and O-C diagrams. The same data used to search for companions are also used to investigate the secular behavior of the pulsations and to directly measure evolutionary timescales for these objects, which turn out to be in the range of several Myr. The data taken within the EXOTIME program cover several tens of months and based on these long-term data we present the detection of a brown dwarf candidate and an exoplanet candidate around our two target stars.

Close substellar companions and the formation of hot subdwarf stars

Stephan Geier (University of Erlangen-Nuremberg, ECAP and Remeis-Sternwarte)

It has been suggested that besides stellar companions, substellar objects in close orbits may be able to trigger mass loss in a common envelope phase and form hot subdwarfs (sdBs). In an ongoing project we search for close substellar companions combining time resolved high resolution spectroscopy with photometry and found some very good candidate systems with brown dwarf companions. One of these objects has a mass close to the planetary

• regime. The implications of these new results for the open question of sdB formation are discussed.

Planets around Hot Subdwarf Stars, or Not?

Richard A. Wade (Penn State University), Brad N. Barlow, Sandra E. Liss,

We will discuss the pulsating sdB star CS 1246 and an eclipsing sdB+dM system, both of which show interesting variations in pulsation or eclipse arrival times, which may be interpreted as indicating the

presence of a planet. We do not claim detection of planets, however. Our main concern is to summarize the need to be cautious about such claims, to seek corroborating evidence, and to analyze other possibilities that may plausibly account for the timing signals in these systems. We emphasize in particular the possibility that a small eccentricity may be present, even in a post-common-evelope binary, and that apsidal motion can then induce a timing variation in the absence of a third body. A third body, may of course be responsible for the small eccentricity, but so may

• ther dynamical causes.

Can Life Develop in the Expanded Habitable Zone Around Red Giant Stars?

• W. C. Danchi (NASA Goddard Space Flight Center), J.-L. Menut, B. Lopez

The distance between a star and its habitable zone, as well as its width, increases with time due to stellar evolution. Currently, there is no clear evidence as to when life actually formed on the Earth, but recent isotopic data suggest that life existed at least as early as 700 million years after the Earth was formed. Thus if life could form and evolve

• ver time intervals of 500-1000 million years, then there could be habitable planets with life around red giant stars.

For a 1 solar mass star, at the first stages of its post-main-sequence evolution, the temporal transit of the habitable zone is estimated to be 1 billion years at 2 AU and around 100 million years at 9 AU. For a 1 solar mass star, after the first ascent along the red giant branch and after the helium flash, there is a stable habitable zone from 7-22 AU for up to 1 billion years during quiescent He core burning. In an initial paper (Lopez, Schneider, & Danchi, ApJ, 2005) we discussed the evolution of the habitable zone for 1, 1.5, and 2 solar mass stars with solar metallicity, and presented results for time periods up to the first ascent along the red giant branch. For this presentation, we discuss the previous results as well as new work including the evolution of the habitable zone during the core He burning phase and the ascent along the asymptotic giant branch for stars from 0.8 to 2 solar masses and for a broad range of metallicities.

Session 1.3 White dwarf planets

Tuesday, January 24 Direct detection of substellar and planetary companions to white dwarfs

Matt Burleigh (University of Leicester)

I will present the latest results from our searches for planetary and brown dwarf companions to white dwarfs through direct imaging observations and photometric surveys, including some exciting recent discoveries. I will discuss the limits on the incidence of such objects at white dwarfs, and as companions to their progenitors. I will also look to future opportunities to investigate the population of substellar and planetary companions to white dwarfs.

Search for giant planets around white dwarfs

Hans Zinnecker (Deutsche SOFIA Institut (DSI) der Universität Stuttgart & NASA Ames Research Center)

We review our NICMOS/HST NIR direct imaging search for resolved self-luminous giant planet companions around the 7 white dwarfs in the Hyades cluster as well as additional imaging observations of nearby field white dwarfs and their progenitors with ground-based NIR adaptive optics (VLT/NACO and Gemini-North/NIRI). We discuss the implications of the non-detections and the potential of future higher angular resolution and higher sensitivity direct imaging mid-IR searches with the JWST. We touch upon Spitzer (and Herschel) unresolved

• bservations of infrared excess emission of putative giant planets around nearby white dwarfs within 2O pc.

The survival of giant planets around intermediate mass Main Sequence progenitors of white dwarfs, which suffer major mass loss during the late stage of their stellar evolution, will also be discussed. There ought to be Jupiter-mass planets around white dwarfs that have survived!

8 Years On: A Search for Planets Around Isolated White Dwarfs

JJ Hermes (University of Texas at Austin)

We have used the 2.1m Otto Struve telescope at the McDonald Observatory to measure the time-of-arrival of non- radial g-mode pulsations in more than a dozen variable DA (ZZ Ceti) white dwarf stars. We have now monitored 13

• f these objects in this way since at least late 2003; we are now sensitive to Jupiter-mass planets around these

isolated WDs out to at least 3 AU. We will discuss the current state of our planet search, including one of our most interesting objects, GD66, which has an (O-C) diagram that is a clear deviation from a parabolic trend, which we would expected from simple WD cooling. We discuss the complicated prospects of a planet around this star, our ensemble results thus far, and briefly introduce some auxiliary science from this survey.

Evidence for a low-mass companion around the extremely hot pre-white dwarf central star WD 0044-121 of the planetary nebula NGC 246

Wei Wang (National Astronomical Observatories of China)

The numerous exoplanet detections during the last two decades have opened the possibility to study the evolution of planetary systems. There remains the challenging question if planets survive the final phase of stellar evolution. To answer this question, we initiated a pilot survey to search for substellar companions around nearby bright white dwarfs with the radial-velocity (RV) technique, using the FEROS instrument at the 2.2m MPG/ESO telescope. We detected a RV variation with a period of ~4 days and a semi-amplitude of 1.85 km/s in the hot white dwarf WD 0044-121. After investigating stellar pulsations and activity, such as a stellar wind, modulated by stellar rotation as the source of the RV variation, we concluded that the RV variation is probably caused by an orbiting low-mass

• companion. We derived the companion minimum mass to be 10.48(2.06) M_Jup and an orbital semi-major axis of

0.046 AU. This finding suggests that giant planets or brown dwarfs can either survive the violent evolution stages or have the chance to be 'born-again' in the dusty disk of an evolved system.

Orbital period variations in eclipsing white dwarf binaries

Steven Parsons (University of Warwick)

Timing measurements of eclipsing white dwarfs in compact binary systems are showing increasingly convincing evidence for the presence of planetary mass companions in orbit around the binaries, some of them multiple. In several cases the planets are in orbits that would have been unstable prior to the formation of the white dwarf and consequent shrinkage of the binary orbit. It is not yet known whether such planets are primordial, and thus require

• rbital shrinkage, or whether they form out of the large mass (~1.5 Msun) ejected during the common-envelope

phase from which the white dwarf emerged, but most of all it is not yet certain that the planets are real. Using results from the 2m robotic Liverpool Telescope and the high-speed camera ULTRACAM, I will show how we are able to measure such precise eclipse times for eclipsing white dwarf binaries. I will also outline some of the difficulties encountered when fitting eclipse time variations. These range from uncertainties in historic times to a lack of constraints for the orbital elements when fitting. I will show how adding relatively small amounts of new data can drastically reduce the allowed parameter space. Finally, I will also show that the new, but growing, class of eclipsing double white dwarf binaries will allow us to test whether the observed period variations in detached WD+MS binaries and CVs are in fact caused by internal processes within the main sequence star.

• 2. DISK OBSERVATIONS

Wednesday, January 25 Debris Disks around Neutron Stars

Geoff Bryden (Jet Propulsion Laboratory)

The discovery of planets around pulsars suggests that neutron stars evolve through some of the same planet-forming stages as their hydrogen-burning parents. In particular, planets suggest disks. While some of the physics is undoubtedly different, the general progression may be the same, where an early phase with a massive planet- forming disk eventually decays into scraps of orbiting debris with much longer lifetimes. In support of this possibility, some young neutron stars do in fact exhibit infrared emission consistent with a thick dust disk heated by a central X-ray source. Observations of older pulsars over a wide range of wavelengths, however, have not detected any longer-lived debris. Despite these non-detections, asteroid belts comparable in mass to our own cannot yet be ruled out.

Ancient Planetary Systems Orbiting White Dwarfs

Ben Zuckerman (University of California, Los Angeles)

Since 1987 we at UCLA have been studying dusty disks that orbit white dwarfs and, since the late 1990s, the atmospheric pollution that results when disk material accretes onto a white dwarf. The now generally accepted model of tidal disruption of asteroids as the origin of the dusty disks was initially developed at UCLA in 2003. The 2007 Keck/HIRES study of highly polluted white dwarf GD 362 revealed 17 elements and demonstrated that, with a sufficiently large telescope, detailed measurements of bulk elemental compositions of extrasolar rocky bodies are

• possible. Today I'll summarize some of what has been learned from past studies of polluted white dwarf

photospheres and how these studies inform astronomy about ancient planetary systems, specifically their ubiquity or lack thereof, their structure, and the elemental composition of the rocky bodies that survive past the asymptotic giant

• branch. The water and volatile element content of these rocky bodies will receive special attention, the volatiles

from our recent ultraviolet study with the COS UV spectrometer on HST of two highly polluted DB white dwarf stars.

Performing autopsies of planetary systems with the WIRED survey and new dynamical models

• J. H. Debes (Space Telescope Science Institute), D.W Hoard, S. Wachter, C. Stark, K.

Walsh, D. Leisawitz, M. Cohen

White dwarfs (WDs) are quite unique laboratories for studying planet formation. Because of their density, effective temperature, and luminosity, WDs are well suited for detecting brown dwarfs, planets, dust, and circumstellar gas in

• rbit. We seek to provide a useful autopsy of interesting WDs in order to better understand planetary systems that

have survived post-main sequence evolution. In particular, we are using observational tools, like the WISE Infrared Excesses around Degenerates (WIRED) Survey, and theoretical tools, such as N-body simulations of planetary systems evolving through post-main sequence evolution, to unearth new information about WD planetary systems. WIRED combines optical, near-infrared, and WISE photometry of known WDs in order to search for infrared excesses due to substellar companions and dusty disks. We have recently searched nearly 18,000 WDs in the preliminary SDSS DR7 WD catalog for infrared excesses, detecting >1500 with WISE. Of those 1500, we find approximately 160 candidate WD+Brown Dwarf and WD+disk systems. We discuss some interesting examples from these candidates. Finding a large number of new dusty disk candidates motivates further work on how such dust disks might form. We also present new dynamical models of asteroid belts interacting with giant planets in

• rder to explain the presence of dust disks around WDs and link them directly to planetary systems similar to the

Solar System. Both approaches provide a rich foundation for future work with the James Webb Space Telescope and the Hubble Space Telescope to fully characterize the composition of terrestrial planet forming regions and directly

image giant planets around nearby WDs.

Transient events from the destruction of planets and smaller bodies

Noam Soker (Technion)

We discuss transient events formed by the destructions of planetary system bodies. In the first process a planet is destructed when it merges with its parent brown dwarf or low mass main sequence star. This process is a scaled down version of more energetic transient events, such as V838 Mon. In the second process the destruction of an asteroid by a WD might be observed as a transient event.

Gaseous debris disks around white dwarfs

Boris Gaensicke (University of Warwick)

About two dozen white dwarfs with dusty debris disks are known, with cooling ages in the range ~100Myr to ~1Gyr. Our understanding of the formation, structure, and evolution of these discs is still hazy, as the amount of information that the shape of the near-infrared excess provides is limited. There are good reasons to believe that in addition to the dust at least some, but maybe all of these disks contain also gas, which would dramatically alter their evolution. We have identified six white dwarfs in which emission lines of the CaII triplet reveal the presence of a gaseous disk component, and I will provide an up-to-date overview of the growing body of observational evidence as well as progress in our modeling of these disks: (1) a thorough assessment of the frequency of such gaseous disks based on the spectroscopic data from SDSS DR8; (2) Spitzer observations of all 6 stars reveal infrared excess, confirming the co-existence of dust and gas, though with some noticeable variations in the strength of the observed excess; (3) detailed abundance analyses based on high-resolution ground-based and HST spectroscopy shows that the circumstellar material is beyond any doubt of rocky nature [though, if time permits, I will show that there appears to be some variation in the abundance pattern that are observed among a larger HST survey of metal-polluted stars]; (4) detailed follow-up spectroscopy of about half of the known white dwarfs found to have dust show *no* sign of CaII emission, even though they are often indistinguishable from the dust-bearing once ... raising the question what causes the gas in some systems, and its absence in others; (5) there is striking evidence that the structure of the gas disks evolves on time scales of months to years, exhibiting on occasions highly complex velocity fields - I will discuss some toy models that are motivated by the observations; (6) a CLOUDY model of debris disks irradiated by the white dwarf provide some insight into their vertical and radial structure, reproduces (most of) the observed emission line, and suggests that the white dwarf in the disk centre is efficiently shielded from the irradiating flux.

Non-LTE Spectrum Models of the gaseous planetary debris disk in SDSS J1228+1040

• S. Hartmann (Institut für Astronomie und Astrophysik Tuebingen), T. Nagel, T. Rauch, K.

Werner

The metal rich, dusty debris disks surrounding white dwarfs do most likely originate from planetesimals or smaller rocky planets being destroyed by the gravitational forces when entering the white dwarf's Roche lobe. With SDSS J122859.92+104033.0 (hereafter SDSS 1228) the first system was discovered, which hosts not only such a dusty but also a gaseous, planetary debris disk. The spectral signature of this gas content provides the only possibility so far, to study the disk's material directly, before it is accreted onto the white dwarf. We present our detailed non-LTE spectrum calculations for SDSS 1228 performed with the Teubingen Acretion Disk code AcDc. Assuming a Keplerian rotating viscous disk, we modeled metallic gaseous rings to study how surface density, effective temperature, and chemical mixture, as well as the radial extension, and disk geometry influence the spectrum. A special focus is set to the CaII IR triplet, being the most obvious disk spectral sign.

SDSS J0738+1835: A DBZ white dwarf that has it all

Patrick Dufour (Université de Montréal)

The presence of large quantities of heavy elements at the surface of high surface gravity white dwarfs is now believed to be the result of accretion from tidally disrupted asteroids or small planets (see also contribution by Ben Zuckerman). Here I will present a detailed photospheric analysis of the most metal polluted white dwarfs known to date, the DBZ SDSS J073842.56+183509.06. Preliminary analysis of this star (Dufour et al., 2010) has shown that it has a total amount of heavy elements equivalent to the mass of Ceres in its convection zone. This object is also surrounded by a warm dusty debris disk as well as by a gaseous disk component. I will discuss our new detailed compositional analysis of SDSS J0738+1835, based on high resolution observations taken with Keck and Magellan, which appear to indicate that the planet that crashed onto this star formed in a low temperature environment. I will also discuss preliminary results on other interesting metal polluted white dwarfs.

Dusty Disks around Hot White Dwarfs: Rejuvenated Debris from Minor bodies that Survived Post-Main-Sequence Evolution

Kate Su (University of Arizona)

Exoplanets and minor-body populations revealed as tenuous debris disks are commonly found around main- sequence (MS) stars of all masses. Theories have long predicted that planetary bodies can survive the ordeal of post- MS evolution as long as they resided more than a couple AU away from their MS host. As the white dwarf cools, asteroids and Kuiper-belt analogs that survived can repopulate the dust reservoir in the system, which can be readily detected as an infrared excess around the stellar corpse. The infrared emission characteristics such as dust temperatures and amount of emission provide insights into the nature of the dust reservoir. The infrared excess discovered around the Helix central star represents a prototype of a post-MS KBO-like disk in the earliest stage of white dwarf evolution. In this talk, I will review the Helix debris system and give a general overview of other dusty disks around hot white dwarfs based on a Spitzer 24 micron survey.

Dust disks around Central Stars of Planetary Nebulae: Subplantery, Circumbinary,

• r Other?

Jana Bilikova (University of Illinois)

Spitzer observations of the hot central white dwarf (WD) of the Helix Nebula have revealed a 90-130 K dust disk at 30-100 AU. This dust disk has been suggested to be produced by collisions among Kuiper Belt-like objects, similar to the dust production around main-sequence stars' debris disks. To find more dust disks similar to that in the Helix, we have carried out a Spitzer 24 um survey of hot WDs and pre-WDs, and an archival Spitzer survey of central stars

• f planetary nebulae (CSPNs). From these two surveys, we have found 13 cases of IR excesses due to extended

emitters that can be afforded only by dust disks or dust clouds. The SEDs and follow-up spectra of these CSPNs show a great diversity in the emission characteristics of their IR excesses, which may imply multiple mechanisms responsible for the excess IR emission. The origin of these dust disks may be complex. In addition to the breakup of KBOs, these dust disks may be formed in binary interactions, and descend from the commonly-observed dust disks around post-AGB binaries, or be associated with a binary companion, as may be the case for CSPN EGB 6. In my talk, I will discuss the physical properties of the dust disks around hot WDs and CSPNs, and relate them to possible physical origins.

• 3. PLANETS AND STELLAR EVOLUTION

Session 3.1 Evolution toward stellar remnant planets

Wednesday, January 25 Planets around evolved stars

Andrzej Niedzielski (Torun Center for Astronomy)

On their way from the Main Sequence (MS) to the stage of a stellar remnant all isolated stars, as well as their planetary systems, undergo a significant evolution. A relatively uneventful MS evolution influences planetary system very little, and its architecture is disturbed mainly by planet-planet interactions. In the red giant phase, the increasing stellar radius influences directly the inner planetary system through tidal interactions and engulfment, and it may change the structure of the outer system. The fast stellar mass-loss additionally weakens the gravitational

• interactions. Late stellar evolution, sometimes very violent, affects substantially the structure of planetary systems
• again. In the case of planetary systems nested in stellar binaries or more complicated systems their structure is

affected by both dynamical interactions with and evolution of the companion stars. The population of planets orbiting evolutionarily advanced stars is not large. The known objects show that planets may either survive all stages of stellar evolution or form again from the matter ejected from stars as a consequence

• f their evolution. In my review I will summarize observations of currently known planetary systems around

evolved stars, and discuss them from the point of view of stellar evolution. I will also discuss observational limitations in studies of evolved planetary systems. As the population of known, slightly evolved sub-giants and giants with planets is most numerous, I will discuss these objects in more detail.

The Evolution of Planetary Systems

Johny Setiawan (Max-Planck-Institut für Astronomie)

The diversity of exoplanets discovered in the last two decades opens an opportunity, not only to find earth-like planets, but also to study the life of planetary systems. The evolution of planetary systems gives an insight to the life (history and future) of our solar system. Moreover, this kind of study can additional information about the presence

• f exoplanets in a wider context, i.e., the formation in the early epoch of the Universe, the origin and the role of the

host star's fundamental stellar parameters. In the last 8 years we have been carrying out a systematical planet search across the HR-diagram, including the young, main-sequence, giant stars and white dwarfs. We obtained some interesting results, which I will present in this conference. Especially, I will give more detail results for the stars in late evolutionary status and other evolved old stars.

Two Populations of White Dwarf Companions

David Spiegel (Institute for Advanced Study)

Planets and other low-mass binary companions face a variety of potential fates as their host stars move off the main sequence and grow to subgiants and giants. Stellar mass loss tends to make orbits expand, and tidal torques tend to make orbits shrink, sometimes to the point that a companion is directly engulfed by its primary. Furthermore, once engulfed, the ensuing common envelope (CE) phase can result in the companion becoming fully incorporated in the primary's envelope; or, if the companion is massive enough, it can eject the envelope and remain parked in a tight

• rbit around the white dwarf core.

We therefore predict two populations of planets around white dwarfs: those that have been through a CE phase and are in short-period orbits, and those that have entirely avoided the CE and are in long-period orbits. I will discuss the calculations that predict this period gap in the distribution of white dwarf binary companions, and will discuss transit searches as a way to probe the inner edge of the gap.

Circumbinary Planets

Frederic "Rick" Hessman (Institut für Astrophysik Göttingen)

One of the most recent surprises in the field of extrasolar planets has been the existence of circumbinary planets. It has taken a while for us to accept the fact, that exoplanets are common around single stars, but the idea that circumbinary planets might be fairly common definitely goes against the standard picture of planetary formation and the straight-forward constraints of planetary system dynamics. Planets around evolved close binaries pose an even greater puzzle, both because it's hard to imagine 1st-generation planets surviving the common-envelope phase in any number and because the formation of 2nd or 3rd-generation planets is difficult to consider theoretically in any detail. I will discuss the current state of our observational and theoretical knowledge of circumbinary planets around evolved close binaries - including the question of whether they really exist and, if so, in what numbers and systems - and outline some of the current challenges and goals.

Planets and Evolved Stars: The low-and Intermediate Stellar Mass Range

Eva Villaver (Universidad Autónoma de Madrid)

Searches for planets orbiting sub-giants and giant stars are revealing a wealth of systems with properties that often differ from those of their main sequence counterparts. Furthermore, the indirect evidence of the possible presence of planets, or at least, their building blocks, around white dwarfs is becoming overwhelming. Giant and white dwarf stars represent the evolutionary endpoint of most of the stars in the Universe, those with main sequence masses between 1 and 8 Msun. In this talk, I will describe how the structural changes that these stars undergo as they run

• ut of nuclear fuel modify the conditions for planet survival and evolution.

Understanding Planet Formation in the Vicinity of Massive Stars

H.W. Yorke (Jet Propulsion Laboratory, California Institute of Technology)

Our theoretical understanding of planet formation is based on the environment of dusty gas circumstellar accretion disks around stars or protostars. Sedimentation of the dust toward the mid-plane and the associated dust coagulation builds up larger particles in the gaseous disk that eventually coalesce into planetesimals. Gravity ultimately draws the planetesimals into solid bodies that are either the terrestrial type planets or the cores of jovian type planets upon which gas can accrete. Massive star formation creates a harsh environment that ultimately shortens the lifetime of gaseous disks of the forming star and of nearby stars. The constraints on planet forming are severe. We examine these constraints in the context of the observations of planetary systems around pulsars.

Star Hoppers: Putting Planets around Evolved Binary Stars

Kaitlin M. Kratter (Harvard - Smithsonian CfA), Hagai Perets

Planets are commonly found in main-sequence binary systems. While these planets may be born on sufficiently tight

• rbits to be dynamically stable, these orbits evolve along with the parent stars. In this talk, I will describe how mass

loss due to stellar evolution can trigger orbital instabilities in such systems. Planets which become unstable can be ejected from the system, collide with either star or even get captured by the secondary. I will discuss the implications of this instability for the observability of planets in evolved binary systems.

The Great Escape II: Exoplanet Ejection from Dying Multiple Star Systems

Dimitri Veras (University of Cambridge)

Extrasolar planets and belts of debris orbiting post-main-sequence single stars may become unbound as the evolving star loses mass. In multiple star systems, the presence or co-evolution of the additional stars can significantly complicate the prospects for orbital excitation and escape. Here, we investigate the dynamical consequences of multi

phasic, nonlinear mass loss and establish a criterion for a system of any stellar multiplicity to retain a planet whose

• rbit surrounds all of the parent stars. For single stars which become white dwarfs, this criterion can be combined

with the Chandrasekhar Limit to establish the maximum allowable mass loss rate for planet retention. We then apply the criterion to circumbinary planets in evolving binary systems over the entire stellar mass phase space. Through about $10^5$ stellar evolutionary track realizations, we characterize planetary ejection prospects as a function of binary separation, stellar mass and metallicity. This investigation reveals that planets are significantly more susceptible to ejection from multiple star systems than from single stars. The former may represent the greater source of free-floating planets.

Are hot Jupiters second-generation planets?

Eduardo Martin (Centro de Astrobiología CSIC-INTA)

Very recently Martin, Spruit, & Tata (2011, A&A, 535, A50) have shown that the abundance and properties of W UMa stars and low mass detached binaries are consistent with being possible progenitors of the host stars of inflated hot Jupiters. The degree of inflation of the transiting hot Jupiters correlates with their expected spiral-in life time by tidal dissipation, and this could indicate youth if the stellar dissipation parameter Q?' is sufficiently low. An up-to- date revision of estimates of the dissipation parameter will be given and tests of this scenario for hot Jupiter formation will be provided in this presentation.

Session 3.2 Debris disks around white dwarfs

Thursday, January 26 Evolution of compact debris disks around metal-rich white dwarfs

Roman Rafikov (Princeton University) Recent discoveries of compact debris disks around metal rich white dwarfs strongly suggest a link between the metal pollution of these stars and the presence of (most likely) planetary circumstellar material around them. I will describe theoretical understanding of the properties and evolution of the compact debris disks - both gaseous and particulate - around white dwarfs. I will demonstrate that radiation of the central star plays important role in driving disk accretion via the Poynting-Robertson effect. It will also be shown that the coupling between the coexisting gaseous and particulate debris disks can give rise to runaway evolution resulting in very large accretion rates of metals onto the white dwarf atmosphere.

New Results on the Frequency and Lifetime of Planetary Debris at White Dwarfs

Jay Farihi (University of Leicester)

Circumstellar disks at single white dwarf stars are signatures of remnant planetary systems, where the star itself betrays the basic chemistry of the disk material. All indications to date point to (pulverized) terrestrial analog parent bodies that are either building blocks or fragments of major rocky planets. I will present the details of recent Spitzer studies of these exo-terrestrial debris rings, including new and cumulative statistics. This research constrains the frequency of rocky planetary systems around intermediate mass stars, and provides limiting masses and empirical chemical data for bodies that comprise solid planets.

Eccentric Planets and Stellar Evolution as a Source of Polluted White Dwarfs

Shane Frewen (University of California, Los Angeles)

A large fraction of white dwarfs appear to be polluted with metals despite their high surface gravities and short diffusion times. The current theoretical model for this pollution is accretion of rocky bodies, perturbed inwards

toward the white dwarf by planets via instabilities caused by mass loss. We examine the stability of test particles in a single-planet system during the main sequence and white dwarf stages within 10 and 20 AU, respectively. In particular, we compare the instabilities that develop before and after the star loses mass to form a white dwarf, a process which causes the semi-major axes of the planet to expand adiabatically. We repeat this process for a range

• f planetary masses and eccentricities, focusing on the number of particles that become unstable and the fraction of

those that impact the central body. We determine that eccentric planets, particularly those with masses below that of Jupiter, are more efficient at delivering material to the central body, while stellar evolution results in a small increase in the unstable region.

Session 3.3 “Second chance” planets around neutron stars

Thursday, January 26 Terrestrial Planet formation around pulsars and solar-type stars

Brad Hansen (University of California, Los Angeles)

I will describe models for the formation of planets around pulsars, based on the accepted paradigm for terrestrial planet formation around solar type stars but applied to theories for the origins of the pulsar planets. Generalizations

• f these models can be applied to anticipate the formation of second generation planetary systems around white

dwarfs as well as shedding light on the initial conditions in our own solar system.

Planets in the Extreme Environments of Neutron Stars

• M. Coleman Miller (University of Maryland)

The discovery of the first extrasolar planets, by Wolszczan and Frail (1992), was highly unexpected because these planets are around a neutron star rather than a normal star. This system, which still holds the record for the lowest- mass extrasolar planet ever detected, seems as inhospitable as one could wish for planet formation or survival. Nonetheless it exists, and there are hints of other neutron star systems with dusty disks that may eventually form planets, as well as a neutron star planet in a globular cluster which was probably produced dynamically. I will review the state of the evidence and models for how planets can form or survive in such trying environments.

• 4. LIFE ON PLANETS AROUND STELLAR REMNANTS

Friday, January 27 Life in the Universe

Andre Maeder (Geneva Observatory)

The frequent consensus of some authors concerning life on planets is more the result of our ignorance than of well- established scientific conclusions. This concerns all terms in Drake’s equation and in particular the biological terms. In addition to the well-known conditions for life as discussed for decades in literature, we review some recent works in astrophysics, geophysics and biology, which show a number of new critical conditions. These may constitute additional bottlenecks for the origin and development of life on a planet, with evidently major differences whether

• ne considers the case of an “intelligent” civilization or bacterial life. Some conditions are very constraining for

planets around stellar remnants. A general underlying question is whether the origin and evolution of life is determined by “contingencies” or by “convergences”. In the first case, random effects would play the leading role; in the second, similar paths in evolution would occur. Great scientific names are associated to both these opposed views. We report some original views of the biologists on the matter.

Life in Extreme Environments

Lynn Rothschild (NASA Ames Research Center)

Life occupies a multi-dimensional niche space, but in the last few decades we have discovered that this envelope for life far exceeds what seemed possible. Boiling acid springs, pH 12 lakes, saturated salt, high radiation and the high pressure depths of the ocean are now known to harbor a variety of life forms. Extremeophiles - organisms that live at the boundaries of the physical and chemical limits for life - have enriched our understanding of life on earth, and the potential for life elsewhere. Some adaptations to life in extreme environments are biochemically straightforward or even convergent, suggesting relative ease in evolution. In astrobiology the interest in studying life in extreme environments includes both understanding the diversity of life on earth, but also the potential for life on other habitable bodies in our solar system. Could the extremophiles on earth allow for the potential for life around stellar remnants?

The white dwarf habitable zone

Eric Agol (University of Washington)

White dwarfs cool to the temperature of the Sun after several billion years at which point their habitable zones shrink to 1/100 of an astronomical unit. This happens to coincide with twice the Roche limit for Earth-density planets, which is about as close as we see exoplanets orbiting other stars. The transit probability is 1%, so if 1% of white dwarfs harbor short-period Earth-like planets, a survey of 10,000 white dwarfs should uncover these. The

• rbital periods are twelve hours while the transits last a couple of minutes, so a wide-field telescope covering tens of

square degrees could cover a dozen or two white dwarfs at a time, completing the survey in a few years. I will discuss the potential properties of such planets, how they might be characterized should they exist, and the prerequisites and pitfalls for such habitable-zone planets being actually habitable.

Habitability of rocky exoplanets

Lisa Kaltenegger (Max-Planck-Institut für Astronomie and CfA)

A decade of exoplanet search has led to surprising discoveries, from giant planets close to their star, to planets

• rbiting two stars, all the way to the first extremely hot, rocky worlds with potentially permanent lava on their

surfaces due to the star's proximity. Observation techniques have now reached the sensitivity to explore the chemical composition of the atmospheres as well as physical structure of some detected planets and find planets of less than 10 Earth masses (so called Super-Earths), among them some that may potentially be habitable. Two confirmed non-transiting planets and several transiting Kepler planetary candidates orbit in the Habitable Zone

• f their host star. Observing mass and radius alone can not break the degeneracy of a planet’s nature due to the

effect of an extended atmosphere that can also block the stellar light and increase the observed planetary radius

• significantly. Even if a unique solution would exist, planets with similar density, like Earth and Venus, present very

different planetary environments in terms of habitable conditions. Therefore the question refocuses on atmospheric features to characterize a planetary environment. We will discuss models for habitability of the planet based on stellar and planet characteristics, from stellar evolution to planetary mass. And observational features of rocky planets in the HZ of their stars can be used to examine if our concept of habitability is correct and how we can find the first habitable new worlds in the sky.

The Habitable Exoplanets Catalog: New tools and methods for planetary habitability assessments.

Abel Mendez (Planetary Habitability Laboratory, University of Puerto Rico at Arecibo)

Habitability metrics can be used to assess and compare the potential for life of exoplanets as a function of many stellar and planetary properties. They provide a system for exoplanets identification, ranking, observational prioritization, and comparisons. Most of these metrics requires stellar and planetary properties that are already available for many exoplanets but models are used otherwise. Here we present various metrics and classifications that help standardize habitability assessments, and they were used as part of our Habitable Exoplanets Catalog. Similar formulations can be constructed for potential habitable exoplanets around more extreme stellar conditions.

Habitable Zone Limits for Dry Planets

Yutaka Abe (University of Tokyo)

The most discussion of habitable planets has focused on Earth-like planets with globally abundant liquid water. For an “aqua planet” like Earth the surface freezes if far from its sun, and the water vapor greenhouse effect runs away if too close. Here we show that “land planets” (desert worlds with limited surface water) have wider habitable zones (HZ) than aqua planets. At the inner edge of the HZ, a land planet has two advantages over an aqua planet because: (i) an unsaturated air at the tropics emits longwave radiation at rates above the traditional runaway limit; and (ii) a dry stratosphere limits hydrogen escape. At the outer limits of the HZ, the land planet better resists global freezing because there is less water for clouds, snow, and ice. Here we describe a series of numerical experiments made using a general circulation model for Earth-sized planets. If other things (CO2, rotation rate, surface pressure) are unchanged, liquid water remains at the poles of a low obliquity land planet until net insolation exceeds 415 W/m2 (170% of modern Earth), compared to 330 W/m2 (135%) for the aqua planet. A low obliquity land planet freezes at 77%, while the aqua planet freezes at 90%. We will discuss the possibility that rapid loss of water changes aqua planets to land planets, and extend the life of habitable world.

Carbon Planets: Overview

Marc Kuchner (NASA Goddard Space Flight Center)

Stellar remnants present unique environments for planet formation, and may host companions with exotic chemistries, like planets made substantially of carbon. I'll provide an overview of carbon planet theory: chemistry, structure and formation scenarios. I'll also describe some recent observations of stellar remnants that have yielded candidate carbon planets.

Carbon-rich Atmospheres of Exoplanets - Discovery, Characterization, and Implications

Nikku Madhusudhan (Princeton University)

Recent advances in observations and theoretical modeling are leading to unprecedented constraints on molecular and elemental abundances in exoplanetary atmospheres. Recently, the first stringent constraint on the atmospheric C/O ratio was reported for a hot Jupiter, revealing a C/O>= 1, namely, a carbon-rich atmosphere. Subsequent studies are indicating that carbon-rich atmospheres may not be uncommon, opening the exotic possibility of carbon-rich planets (CRPs). Carbon-rich planets present a new regime in atmospheric chemistry and temperature structure, planetary interiors, planet formation, and astrobiology. In this talk, I will first present an overview of observational and modeling techniques that enable us to measure C/O ratios in extrasolar planets, thereby helping in the search for carbon-rich planetary atmospheres. I will then discuss some key observable properties of carbon-rich planets, in particular their extreme atmospheric chemistry and thermal inversions, which motivate a new classification scheme for irradiated giant planets which accommodates CRPs. Finally, I will discuss the implications of the discovered carbon-rich atmospheres in exoplanets for planet formation scenarios, planetary interiors, and astrobiology. I will end by discussing future prospects in observations and theory of Carbon-rich atmospheres in exoplanets.