Splinter Abstracts

"Spectral Diagnostics of Hot Plasma from Cool Stars"
Nancy Brickhouse, Harvard-Smithsonian Center for Astrophysics

EUV and X-ray spectra tell us about the physical conditions in the hot coronae, in particular temperature, density, elemental abundances, opacity, and velocity. The values derived from spectroscopy inform our models of magnetic structure, accretion shocks, and hot winds. But two issues must always be kept in mind: (1) the methods used are often indirect and inferential, and make a lot of assumptions; and (2) the fundamental atomic data have flaws which are often not taken into account. The proposed splinter session will address both of these issues for topics of recent interest. This session also emphasizes the solar/stellar connection. A summary of this session will be provided to the CS14 Proceedings by N. Brickhouse.

The session will address three critical problems. Each problem will be discussed by a panel of 3 scientists. The panelists will briefly describe how spectroscopic measurements are used to determine a physical property or to infer some physical process. Particular emphasis will be given to the underlying systematic uncertainties. Following their presentations, the audience will be asked for comments.

I. Coronal structure (temperature, density, opacity)

The recent literature has pointed out problems with the "classic'' He-like G-ratio, differences among densities derived using different diagnostics (are stellar coronae really as dense as solar flares?), and temperature discrepancies among Fe lines from the same ionization state. A concerted effort in laboratory astrophysics and atomic theory to address problems in fundamental X-ray spectroscopy was highlighted at NASA's Laboratory Astrophysics Workshop in Las Vegas this spring. Atomic theory is converging on experiment for some important diagnostic line ratios. What is the status of these calculations? What is the impact on coronal research? What does the sun tell us about individual loop structures? Can these be extrapolated to stars? For the case where we think the atomic data are ok, how well do our methods work?

II. Elemental abundances in solar and stellar coronae

For reasons still not well understood, coronal abundances do not in general reflect the underlying photospheric abundances. How reliable are the measurements of abundances? How much do absolute or relative abundances depend on the emission measure distribution modeling?

III. Velocity measurements for high temperature plasma

Chandra HETG can measure Doppler shifts to an accuracy of <25 km/s. The SOHO spectrometers routinely measure velocities of a few to 10's of km/s. Radial velocity studies are useful to constrain the location[s] of the emitting regions in stars. In conjunction with eclipse mapping or flare occultation, even more information can be obtained. Doppler shift measurements indicate the detailed dynamics of solar structures. Line widths are also potentially useful diagnostics for non-thermal broadening. What can we learn about coronae from velocity studies?

"The Formation of Low-Mass Protostars and Proto-Brown Dwarfs" [Splinter home page]
Juergen Steinacker, MPIA Heidelberg, Germany

Star formation is one of the great four themes of 'Origins' studied in astronomy today, and special attention is attributed to the formation of low-mass stars like our own sun. Low-mass stars are thought to form from the collapse of a low-density interstellar molecular cloud, producing a high-density core which evolves into a flattened proto-planetary disk through which material is accreted on to the growing central object.

Large ground-based telescopes and currently active satellite observatories like HST, Chandra, XMM, and most outstandingly Spitzer are delivering a wealth of new details, partially forcing us to re-conceive our conceptions of star formation. At the same time, these new data are preparing the ground for ALMA and Herschel, which will come online in the near future.

The advanced numerical simulations of the complex evolution of collapsing low-mass cores are about to enter a new era with the explicit inclusion of heating and cooling by radiative transfer and with multi-wavelengths modeling of high-resolution images.

However, despite all of these new high-resolution observations and simulations of low-mass star forming regions, the main controlling agents of the early phase star formation process remain highly debated.

The main goal of the splinter session is to highlight ongoing progress in tackling the controlling physical processes of the formation of low-mass proto-stars and proto-brown dwarfs.

The oral presentations are planned to address the main physical processes gravitational collapse, turbulence, magnetic fields, radiation, chemistry, and jets. Detailed work should be presented in posters which are available during the CS14 meeting and which is summarized in a dedicated talk. The final discussion has the objective to consolidate possible projects for improving the progress in the identification of the controlling agent of early low-mass star formation.

We plan to have 8 contributed presentations (12+3 mins) covering highlights of current research on the formation of low-mass protostars and proto-brown dwarfs with an outlook of what can be expected in the next year.

We plan to have the poster presentations proposed for the splinter to be circulated by email well before the session. A summarizing talk will address all posters and their implications for the formation of low-mass protostars and proto-brown dwarfs (12+3 mins). The last 25 mins are devoted to a dedicated discussion about progress in the field by current and planned projects.

"Mining the next generation of surveys for cool star science" [Splinter home page]
David Pinfield, Centre for Astrophysics Research, University of Hertfordshire
Michael Liu, Institute for Astrophysics, University of Hawaii
Hugh Jones, Centre for Astrophysics Research, University of Hertfordshire

Cool star science will benefit greatly in the near future from a variety of major new surveys that are just commencing, or about to start in the next few years. These surveys will have a large and broad impact both on cool star science, and the way cool star science is done. This splinter session is designed to educate the larger community about the survey resources soon to become widely available, and how these will change the field of cool stars. New surveys such as GALEX, UKIDSS, VISTA and WISE will provide the community with multi-band UV-midIR wide-field imaging across much of the sky, and other new facilities such as Pan-STARRS, SkyMapper and SuperWASP (as well as GALEX) will explore time-domain science for cool stars.

These new facilities will allow extensive study of a large range of cool star phenomena, from very hot and violent coronal/flare activity, to extremely cool brown dwarfs with temperatures approaching the planetary regime. Time domain data will reveal information about cool stars in multiple systems and their fundamental properties (via the transit method), as well as the variability intrinsic to individual cool stars. Also, proper motion and parallax will become increasingly powerful discovery tools in some time domain surveys.

It is important that the cool star community is aware of these new capabilities, in order to take advantage of them in the most effective way. To this end, our proposed splinter session would be structured into three main sections: (i) A series of invited talks on cool star science with large-scale datasets generated by GALEX, UKIDSS, VISTA, WISE, Pan-STARRS, SkyMapper and SuperWASP. (ii) A number of contributed talks focusing on new cool star research that is or will soon be exploiting large scale survey facilities. (iii) The session will close with a summary/perspective from an expert in the field, involving audience discussion about the impact of new surveys on cool star science.

1h 30m for invited talks: 7 x 10-15 mins (incl q&a)
1h 10m for contributed talks: 6 x 12 mins (incl q&a)
~15 minutes for a summary/perspective discussion time

"Stellar Ages" [splinter home page]
Eric Mamajek, Harvard-Smithsonian Center for Astrophysics

Stellar ages remain one of the most poorly constrained, but most desired, astronomical quantities. The sources of hazard in assigning ages to individual field stars are plentiful, including, but certainly not limited to: input physics and input abundances to theoretical models, systematic errors in observations of age diagnostics, dispersion of age diagnostics in coeval samples, intrinsic variability of age diagnostics in the stars themselves, erroneous cluster/association memberships, unresolved stellar multiplicity, etc. The primary focus of this session's talks is recent results relevant to the calibration and estimation of ages for cool stars.

Potential splinter session topics/themes:

Ages splinter session will be held Thursday, November 9, 2006. All contributed talks and review talk are 12 min plus 3 min for questions.

"Disks around Cool Stars and Brown Dwarfs" [Splinter home page]
Daniel Apai, University of Arizona, and Kevin Luhman, Penn State University

The aim of the session is to present the newest results and organize them into an evolutionary sequence contributing toward the understanding of planet formation around cool stars. The discussion-oriented session will be led by key speakers and summarized in a written review by the convenors Apai and Luhman.

Understanding the properties of planetary systems around cool stars requires answering four fundamental questions: How frequent are disks around cool stars and brown dwarfs? How often do these disks evolve into planetary systems? What is the least massive star that can harbor planetary systems? How will the architecture of planetary systems vary with the varying stellar and disk parameters?

These exciting questions motivated substantial observational and theoretical effort since Cool Stars 13 and significant progress has been achieved partly by the Spitzer Space Telescope. These studies and results include large–scale thermal infrared imaging demonstrating that about 50% of the young brown dwarfs are surrounded by warm dust disks [e.g. 1] and evidence that disks can be found even around planetary–mass objects [2]. Spitzer infrared spectroscopy has revealed surprisingly processed dust in the inner brown dwarf disks, resembling dust at the epoch of the comet–formation in our Solar System [3]. Optical and near–infrared spectroscopy identified a correlation between stellar mass and accretion rate extending from Herbig stars to young brown dwarfs [4,5].

Recent years brought mounting evidence for planetary systems around very low-mass stars and even brown dwarfs: the direct imaging of the faint companion of 2MASS1207 demonstrated the presence of planetary-mass objects on wide orbits around brown dwarfs [6,7]; radial velocity surveys of M-stars identified 4 close-in giant planets [8] and the direct imaging of the debris disk around the nearby M--dwarf AU Mic highlighted the existence of giant planets and planetesimals [9,10]. Gravitational lensing experiments detected a 5 Earth-mass planet around an M-dwarf, suggesting that cool stars may harbor terrestrial planets more frequently than their more massive counterparts do [11].

Motivated by the observations, intense theoretical work explored the efficiency of planet formation around M–dwarfs [e.g. 12,13] and brown dwarfs [e.g. 14] and the accretion rate–stellar mass correlation [e.g. 15]. The discoveries and the emerging understanding of disk evolution and planet formation around cool objects highlighted the potential of comparative disk studies. This rapidly developing field will greatly benefit from a forum that brings together its yet diverse community.

The splinter session proposed here aims to provide a venue for the community studying circumstellar disks around cool stars and brown dwarfs to: i, review the latest results from Spitzer, HST, and ground-based facilities; ii, cast these results in a coherent evolutionary sequence; iii, discuss the recent results and their implications in detail, developing a better understanding of the processes. The proposed session will be dominated by 15-minute discussions on eight key topics: protostellar phase, disk frequency and life time, disk structure and mineralogy, disk masses, transition disks, planet formation, and debris disks. Each topic will be introduced in a 6-minute review by an expert.

References: [1] Luhman et al. 2005 ApJL 631, 69 [2] Luhman et al. 2005 ApJL 620, 51 [3] Apai et al. 2005 Science 310, 834 [4] Muzerolle et al. 2005 ApJ 625, 906 [5] Natta et al. 2004 A&A 424, 603 [6] Chauvin et al. 2005 438, 25 [7] Extrasolar Planets Encyclopedia [8] Liu 2004 Science 305, 1442 [9] Kalas et al. 2004 Science 303, 1990 [10] Beaulieu et al. Nature 2006 439, 437 [11] Boss 2006 ApJ 643, 501 [12] Laughlin et al. 2004 612, 73 [13] Lodato & Clarke 2005 MNRAS 353, 841 [14] Armitage et al. 2006 ApJ 639, 83 [15] Dullemond et al. 2006 ApJ, in press

The proposed session will consist of the discussion of 8 topics following the evolution of disks around cool stars from the protostellar through the protoplanetary to the debris disk phase, with special emphasis on the formation of planetary systems. Each topic will be introduced in a 6-minute review of the field by a leading expert bridging to a 15-minute open discussion of the participants of the session. The reviewer will also actively participate in the following discussion.
The session will start with a very brief 2-minute welcome and will include a 10-minute break.

"Cool Stars in Hot Places: The Role of Environment in the Formation of Low Mass Stars and Planetary Systems"
S.T. Megeath, University of Toledo

It is well established that cool stars form in a range of environments. In contrast to young hot stars, which are almost always found in dense clusters, cool stars form both in relative isolation within cold dark clouds as well as in dense clusters with hundreds of low and high mass stars. In all of these environments, cool stars are thought to dominate in both number and total stellar mass. This range of environments raises interesting questions regarding the formation of cool stars. How does the environment affect the properties of the nascent stars? Does environment influence the initial conditions of planet formation (or prevent planet formation) by perturbing primordial disks around cool stars? Is there a "typical" environment for cool star formation? In what environment did our sun form in?

There are good reasons to believe that environment plays a significant role in both the formation of low mass star and in the subsequent formation of planets around these stars. Numerical simulations of the formation of clusters predict that dynamical interactions between protostars are important as the protostars compete to accrete gas from the surrounding cloud. During the pre-main sequence phase, dynamical interactions may influence planet formation by stripping disks around young stars. Radiation from hot stars may play an even more important role. HST and Spitzer observations have shown cool stars forming in pillars of molecular gas sculpted by UV radation from neighboring OB stars. Once these stars are enveloped by the HII region, HST observations and theoretical analyses have shown that the UV radiation can evaporate the circumstellar disks, eroding away the outer disks. The effect of hot massive stars on cool star and planet formation is given particular importance by recent analysis of short-live radionuclides in meteorites. These results provide strong evidence that the Sun and Solar System formed in close proximity to a massive star that went supernova very near the time of the Sun's formation.

The role of environment is becoming an essential topic for any discussion on cool star formation. Recent progress on this topic is being driven in large part by observations from Spitzer and the other Great Observatories. Spitzer has completed surveys of ten molecular clouds in the nearest 1 kpc, and can identify both clustered and isolated young stars by the presence of infrared excesses from circumstellar disks and/or envelopes. These observations are being complemented by Chandra observations which identify young cool stars through their elevated X-ray emission. With their ability to identify isolated stars, these two observatories are providing information on the demographics of cool star formation, which, unlike previous near-IR surveys, are not biased towards dense clusters. These results are complemented by a decade of HST observations which show the impact of hot stars on cool star formation and early evolution. The goal of this splinter session is to discuss our current understanding of the demographics of cool star formation, the influence of environment on the star and planet formation implied by these demographics, and the most likely formation environment of the sun. The hope is to move toward a consensus on the relative importance of isolated vs clustered star formation (at least at the solar circle in the current epoch), and how much the typical low mass star is affected by its environment (e.g., what are the typical fluxes of UV radiation impinging on young stars and forming solar systems, and what effects do they have).

We will have four main review talks. We will then have time for two short contributed talks. Finally, we will have a moderated discussion. We would like the review speakers, moderator, contributed talk speakers, and audience participate. Audience members can submit a one viewgraph slide to display a point during the discussion.

Review talks:

Jeff Hester: Constraints on the formation environment of the Sun from astronomical observations and meteoritics

Tom Megeath: Spitzer surveys of molecular clouds and the formation environment of low mass stars

Fred Adams: The influence of the star forming environment on planet formation: theory

John Bally: The influence of the star forming environment on planet formation: observations

"Habitability and Life on Planets Around Cool Stars" [Splinter home page]
Charles Beichman, Michelson Science Center; Wesley Traub, Jet Propulsion Laboratory, and Malcom Fridlund, European Space Agency

What are the astrophysical properties of stars that might lead to the formation and evolution of habitable planets and ultimately to the genesis of life itself? Cool Stars XIV represents a gathering of experts in the properties of stars that bracket those of our own sun with its retinue of planets: younger or older, more or less massive, single or multiple, richer or poorer in various elements, quiescent or active at UV or X-ray wavelengths, with or without massive Kuiper or asteroid belts. All these properties pertain to the suitability of “Cool Stars” as abodes for planets and life.

We propose a 3 hour session devoted to a discussion of these topics. The session would be built around 2-3 invited papers (30 minutes in length), a number of contributed papers (15 minutes in length), and posters (each with a 2 minute pop-up summary). A wrap-up panel discussion would end the session (and the conference) and could include a beer and popcorn social event paid for out of non-conference funds.

"Sub-Stellar Twins: Binarity in the Brown Dwarf Regime"
Ray Jayawardhana, University of Toronto, and Herve Bouy, University of California at Berkeley

Over the past decade, large numbers of very low mass stars and brown dwarfs have been identified in the solar neighborhood, young clusters and star-forming regions. For a variety of reasons, investigating the frequency and nature of binaries and multiple systems among them is one of the most exciting areas of cool star research today. For one, binary properties of brown dwarfs could be an important diagnostic of sub-stellar origins. For another, binaries constitute excellent laboratories for testing evolutionary models of very low mass objects. This splinter session will bring together researchers to discuss the latest findings and prospects for the near future. There have been a number of dramatic advances in our understanding of brown dwarf binarity within the past couple of years. For example, a planetary mass companion has been detected next to a nearby young brown dwarf, and confirmed through common proper motion and infrared spectroscopy. The first eclipsing brown dwarf binary system was announced within the past year. High angular resolution imaging surveys, using adaptive optics on 8-meter-class telescopes and the Hubble Space Telescope, are deriving the binary frequency, mass ratios and separations with sizeable samples of field and young objects; Astrometric follow up of several resolved systems is underway to derive dynamical masses. Radial velocity searches are starting to provide constraints on tight binary systems. The current pace of discovery is truly remarkable, and the session could serve as an opportunity to take stock as well as to spur on novel ideas and new collaborations. As one can see from the participant list below, many of the leading players in recent and on-going research efforts have indicated their intention to attend. The advent of new instrumental capabilities (such as LGS AO at Keck and VLT, CRIRES at VLT) is another reason why this session is timely.

We suggest a split format for this session. First, we will have a series of short talks (~10 min), reporting on the latest results in this rapidly evolving field. Some of these talks have been offered already, and we expect (and welcome) a few more after the official announcement of the splinter sessions. We will also welcome very short, last-minute contributions (1 transparency, 2 min) from the audience. Finally, we expect to hold a panel discussion with audience participation on the implications of the findings to date on brown dwarf formation scenarios.

"Coronal Structure of Pre-Main Sequence Stars"  [splinter home page]
Moira Jardine, University of St Andrews

The study of pre-main sequence stellar coronae is undertaken in many different wavelength regimes, with apparently conflicting results. X-ray studies of T Tauri stars suggest the presence of loops with a range of sizes ranging from less than a stellar radius to 10 stellar radii. Some of these stars show a clear rotational modulation in X-rays, but many do not and indeed the nature of this emission and its dependence on stellar mass and rotation rate is still a matter of debate. Some component of it may come from the accretion shock, but the location and extent of the accretion funnels (inferred from optical and UV observations) is as much of a puzzle as the mass accretion rate that they carry. Equally central to the spin evolution of the system is the loss of mass and angular momentum from the system in either jets or winds. Linking all these different features is the magnetic field. Recent observations suggest the presence of structure on many scales, with a complex, multipolar field on small scales near the surface co-exisiting with a much simpler field structure on the larger scales at which the stellar field may be linking onto a surrounding disk. Some recent models suggest that the open field lines which are responsible for carrying gas escaping in winds and jets may also be responsible for much of the infalling accretion flow.

The aim of this splinter session is to bring together the most recent results from these different wavelength regimes to see if a consistent picture emerges which can shed light on the structure of the coronae of these young objects.

We will divide the 1.5 hours allocated into three sections highlighting recent advances in the structure of: the surface and coronal magnetic field, the accretion funnels/outflow regions and the large-scale X-ray corona. Each section will comprise two or three short talks followed by a discussion period (which may include short single-overhead 2 minute contributions of very recent results).