Planet Formation in the Outer Solar SystemKenyon, Scott J.
doi: 10.1086/339188pmid: N/A
This paper reviews coagulation models for planet formation in the Kuiper belt, emphasizing links to recent observations of our and other solar systems. At heliocentric distances of 35–50 AU, single‐annulus and multiannulus planetesimal accretion calculations produce several 1000 km or larger planets and many 50–500 km objects on timescales of 10–30 Myr in a minimum‐mass solar nebula. Planets form more rapidly in more massive nebulae. All models yield two power‐law cumulative size distributions, NC∝r-q with q = 3.0–3.5 for radii r≳10 km and NC∝r-2.5 for radii r≲1 km. These size distributions are consistent with observations of Kuiper belt objects acquired during the past decade. Once large objects form at 35–50 AU, gravitational stirring leads to a collisional cascade where 0.1–10 km objects are ground to dust. The collisional cascade removes 80%–90% of the initial mass in the nebula in ∼1 Gyr. This dust production rate is comparable to rates inferred for α Lyr, β Pic, and other extrasolar debris disk systems.
Selection of High‐z Supernova CandidatesDahlén, Tomas; Goobar, Ariel
doi: 10.1086/341046pmid: N/A
Deep, ground‐based, optical wide‐field supernova searches are capable of detecting a large number of supernovae over a broad redshift range up to z∼1.5. While it is practically infeasible to obtain spectroscopic redshifts of all supernova candidates right after their discovery, we show that the magnitudes and colors of the host galaxies, as well as the supernovae, can be used to select high‐z supernova candidates for subsequent spectroscopic and photometric follow‐up.Using Monte Carlo simulations we construct criteria for selecting galaxies in well‐defined redshift bands. For example, with a selection criterion using B−R and R−I colors we are able to pick out potential host galaxies for which z≥0.85 with an 80% confidence level and with a selection efficiency of 64%–86%. The method was successfully tested using real observations from the Hubble Deep Field.Similarly, we show that the magnitude and colors of the supernova discovery data can be used to constrain the redshift. With a set of cuts based on V−R and R−I in a search to mI∼25, supernovae at z∼1 can be selected in a redshift interval σz≤0.15.
On the Nature of Stars with PlanetsReid, I. Neill
doi: 10.1086/339257pmid: N/A
We consider the metallicities and kinematics of nearby stars known to have planetary‐mass companions in the general context of the overall properties of the local Galactic disk. We have used Strömgren photometry to determine abundances both for the extrasolar planet host stars and for a volume‐limited sample of 486 F, G, and K stars selected from the Hipparcos Catalogue. The latter data show that the Sun lies near the modal abundance of the disk, with over 45% of local stars having supersolar metallicities. Twenty of the local stars (4.1%) are known to have planetary‐mass companions. Using that ratio to scale data for the complete sample of planetary host stars, we find that the fraction of stars with extrasolar planets rises sharply with increasing abundance, confirming previous results. However, the frequency remains at the 3%–4% level for stars within ±0.15 dex of solar abundance and falls to ∼1% only for stars with abundances less than one‐half solar. Given the present observational constraints, both in velocity precision and in the available time baseline, these numbers represent a lower limit to the frequency of extrasolar planetary systems. A comparison between the kinematics of the planetary host stars and a representative sample of disk stars suggests that the former have an average age that is ∼60% of the latter.
Simulating Spectrophotometric Fluctuations of p‐Mode Oscillations in Solar‐like StarsTycner, Christopher; Lester, John B.
doi: 10.1086/339256pmid: N/A
The solar‐like spectrophotometric variations due to nonradial oscillations were simulated using a series of synthetic spectra computed and interpolated from stellar model atmospheres, each in complete equilibrium but at varying effective temperatures. The simulations are in good agreement with observations of the Sun done by others. We have demonstrated how the p‐mode signal is distributed as a function of wavelength between 350 and 1000 nm and more specifically how most of the signal is concentrated at shorter wavelengths. We attribute this to the high density of spectral lines at shorter wavelengths, as well as the tendency of the majority of the lines to weaken with increasing effective temperature. Our simulations are also in agreement with the observational studies that report that stronger lines show larger relative variations. We also reproduce the observed exceptions to this trend for lines such as Balmer lines and Ca ii H and K.After simulating a sample observing run, we show that it is very advantageous to take a ratio of two spectral bands, observed simultaneously, that exhibit completely different fractional changes. This is especially important for ground‐based observations that need to suppress scintillation noise and any other intensity fluctuations. Although strong absorption lines could be used for this purpose, a much better contrast can be obtained by using a wider spectral region, say between 350 and 500 nm, in conjunction with a region at much longer wavelengths, for example, in the 800 nm region. Our simple treatment of solar‐like oscillations also indicates that there is no signal loss due to lower resolution, since no single spectral line offsets the shift in the continuum at solar temperatures, as long as only the photometric signal, and not velocity shifts, is the primary interest.
The Ultraviolet Light Curve of LMC X‐4: X‐Ray Heating of the O Star and Accretion DiskPreciado, Michael E.; Boroson, Bram; Vrtilek, Saeqa Dil
doi: 10.1086/339254pmid: N/A
We present an archival study of ultraviolet spectra of the X‐ray binary LMC X‐4 obtained with the IUE satellite. We fit these spectra with models that incorporate the X‐ray heating of the O star and accretion disk. A systematic analysis of the UV continuum confirms the general picture of an O star that fills its Roche lobe and is heated by X‐rays from the neutron star. About 5% of the UV emission arises in an accretion disk, which may precess with a ≈30 day period. We measure the mass transfer through the accretion disk and attempt to relate this quantity to changes in the pulse period and disk precession. The principal source of uncertainty in our model results from the choice of the 30 day disk precession ephemeris. We examine the RXTE All‐Sky Monitor data for LMC X‐4 to attempt to clarify the variability of the 30 day period. We find no evidence for additional heating of the O star or disk as the result of an X‐ray flare observed with IUE and EXOSAT in 1983.
Imaging Simulations of Large‐Scale Flux Recovery at Millimeter WavelengthsHelfer, Tamara T.; Vogel, Stuart N.; Lugten, John B.; Teuben, Peter J.
doi: 10.1086/339189pmid: N/A
We present multiple‐field imaging simulations that explore the issue of large‐scale flux recovery using five current and future millimeter‐wavelength interferometers. The simulations show that nonlinear deconvolutions routinely applied to interferometric maps interpolate and extrapolate to unsampled spatial frequencies and thereby reconstruct much larger scale structures than an analytical treatment of the flux recovery issue would suggest. We show that the fraction of flux recovered for a given observation is a function of the signal‐to‐noise ratio (S/N) of the map; however, even for S/Ns as low as 3, a deconvolved map reconstructs more flux than an un‐deconvolved map. Both the noise‐free and the noise‐added simulations demonstrate that in order to make accurate maps of even moderately large (≳20″) sources at millimeter wavelengths, it is generally necessary to include single‐dish (“total‐power”) or very short spacing data. We demonstrate that for high‐S/N data, how well an individual telescope recovers large‐scale structure for a mosaiced observation is more closely related to the minimum distance between its dishes, Smin - D, than to the minimum center‐to‐center distance, Smin. For a source that is large in one dimension but small in another (e.g., an elliptical Gaussian), the simulations show that the flux recovery is more closely determined by the small dimension than by the long dimension. This may help with the real imaging of spiral galaxies, where the rotation tends to confine the emission in any given channel map to a relatively small region in one dimension. These simulations were motivated by our work with mosaics from the Berkeley‐Illinois‐Maryland Association Survey of Nearby Galaxies (BIMA SONG), but the results apply generally to millimeter‐wavelength interferometric images.