摘要:

The concept of aperoi kosmoi (multiplicity or plenitude of worlds) has had at least four meanings at various times, two capable of yielding images and two not. We explore here the several meanings and their connections with modern astronomical ideas, focusing finally on the one in the minds of the organizers of the present conference. There seem to be at least two dozen ways of potentially detecting or limiting the incidence of “other worlds,” in the sense of potentially habitable planets orbiting other stars, a handful of which have led to detections, false alarms, or both. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774491

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Doppler monitoring of a sample of 1330 stars with a precision of 3 m s−1is discussed. Seventy five planets residing in 65 systems have been discovered within this sample, a detection rate of 5&percent;. Eight multiple systems are found in the sample, and roughly half of the systems with one known planet appear to harbor additional companion(s). The incidence of “hot jupiters”, orbiting within 0.1 AU is 1.0 &percent;. There appears to be a “pile up” of planets at P=3 days. Planets with even shorter periods could easily be detected but none was found indicating they are exceedingly rare. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774492

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

While the study of extrasolar planetary systems has made astonishing progress during the last decade we are very much at the beginning of this new topic. Our study so far has only been sensitive to gas giant extrasolar planets. The 110 or so that we have discovered probably represent the relatively close‐in subset of the population of gas giant planets. Here we consider some of the questions that arise from the study of the properties of this subset. In particular we focus on the semimajor axis of extrasolar planets. Values of semimajor axis are a key parameter because observationally they are well determined and theoretically they are a key test of planet formation and migration. While many features of the semimajor axis distributions are well produced by models, features such as the apparent drop in eccentrities and metallicities towards large values of semimajor axis are not yet reproduced by simulations. A full understanding of the statistics of extrasolar planets awaits the discovery and study of a much broader range and larger sample of planets as well as continued intensive work on numerical simulations to produce more physical models of formation, migration and interaction. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774493

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Precise radial velocity measurements have led to the discovery of ∼ 100 extrasolar planetary systems. It is important to understand the uncertainties in the orbital elements that have been fit to these data. While detections of short‐period planets can be rapidly refined, planets with long orbital periods will require decades of observations to constrain the orbital parameters precisely. Already, in some cases, very different orbital solutions provide similarly good fits, particularly for long‐period and multiple planet systems. Thus, it will become increasingly important to quantify the uncertainties in orbital parameters, as future discoveries are likely to include many planets with long orbital periods and in multiple planet systems.Markov chain Monte Carlo (MCMC) provides a computationally efficient way to quantify the uncertainties in orbital elements and to addressspecificquestions directly from the observational data rather than relying on best‐fit orbital solutions. MCMC simulations reveal that for some systems there are strong correlations between orbital parameters and/or significant non‐Gaussianities in parameter distributions, even though the observational errors are Gaussian. Once these effects are considered the actual uncertainties in orbital elements can differ significantly from the published uncertainties. This has implications for the interpretation of the orbits of extrasolar planets. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774494

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present an overview of our ongoing systematic search for wide (sub)stellar companions around the stars known to host rad‐vel planets. By using a relatively large field of view and going very deep, our survey can find all directly detectable stellar and massive brown dwarf companions (m>40MJup) within a 1000 AU orbit. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774495

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Accretion disks are pivotal elements in the formation and early evolution of solar‐like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve the mystery of the formation of our Solar System. This chapter focuses on observational studies of circumstellar disks associated with pre‐main sequence solar‐like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of typical star forming regions (e.g., ∼140pc for Taurus), a planetary system like ours (with diameter ≃ 50AU out to Pluto, but excluding the Kuiper belt) subtends only 0.35″. Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks.Fortunately, capable instruments providing 0.1″ resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near‐infrared from ground‐based adaptive optics systems, to the millimetric range with long‐baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low‐mass stars has made a gigantic leap forward in the last decade. In the following pages I will attempt to give an overview of the structural and physical parameters of protoplanetary disks that can be estimated today from direct observations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774496

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The environment of the nearest Herbig Ae star has been investigated through a program of multi‐wavelength, high contrast and high spatial resolution imagery, FUV through optical integrated light spectroscopy, and FUV spatially resolved spectroscopy. HD 104237 is the primary of a 5 Myr old aggregate of at least 4 PMS stars, 2 of which in addition to HD 104237 have IR excesses indicating the presence of dust disks. HD 104237 is actively accreting, and is driving a bipolar outflow (HH 669) which can be traced 2.65″ from the star and which is viewed at an inclination of18−11+14°. The counterjet can be traced no closer than 0.6″ (79 AU) from the star, providing a firm upper limit to the size of the disk. The absence of spatially extended H2emission, FUV reflection nebulosity, and mid‐IR PAH emission features are all consistent with dust settling and the presence of a geometrically shadowed disk. The combination of proximity, low reddening, and the high density of disks in the HD 104237 association make this group of stars an ideal laboratory for probing the comparative evolution of planetary systems. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774497

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Results are described from observations of submm CO emission from isolated young stars with an infrared excess. These include both Vega‐excess and isolated Herbig AeBe stars, ie those at the transition between the formation stage and the main sequence. Of those detected, more than 60&percent; show double‐peaked profiles, interpreted as emission from rotating gas disks. The spectra of three objects are compared with a basic disk model. HD 141569 has evidence of a double‐ring gas structure, with radii of 90 and 250 au — similar to that seen in scattered light. MWC480 has an asymmetric line shape, interpreted as a non‐axisymmetric disk temperature distribution. Finally the debris disk HD 9672 shows a broad line from a relatively compact disk or ring.This molecular gas is found in stars of ages up to 10–20 Myr, and its’ removal from the disk signifies the end of the accretion and the start of the collision‐dominated phase of disk evolution. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774498

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The recent discovery of the 0.8 M⊙highly iron‐deficient star HE0107‐5240 indicates that solar systems probably form in the very early universe. We discuss some implications of this discovery. Massive stars are predicted to be more common in the early universe than at the present epoch. We describe previously unpublished calculations of massive protostars. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774499

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present high resolution observations of the intensity and velocity fields of the embedded cores NGC 1333 IRAS2, NGC 1333 IRAS4, and L1448N as mapped by theJ= 1 → 0 rotational transitions of C18O, H13CO+, and N2H+. These lines are optically thin and trace the core kinematics over a range of critical densities. We find that thermal broadening is insufficient to explain the emission line widths. Moreover, the behavior of the line widths as a function of spatial resolution is consistent with the turbulent MHD model clouds created by Ostriker, Stone, and Gammie. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1774500

出版商:AIP    

年代:1904

数据来源: AIP