Astronomy. How old is that star? Soderblom, David R
Science (American Association for the Advancement of Science),
2009-Jan-02, 20090102, Letnik:
323, Številka:
5910
Journal Article
Recenzirano
Despite being fundamental in determining its physical state, a star's age cannot be measured directly, and estimation methods are imprecise.
We report the detection of dust emission at submillimeter wavelengths from HD 107146, a G2 V star with an age estimated to lie between 80 and 200 Myr. The emission is resolved at 450 mu m with a size ...300 AU x 210 AU. A fit to the spectral energy distribution gives a dust temperature of 51 K and a dust mass of 0.10 M sub(o+). No excess emission above the photosphere was detected at 18 mu m, showing that there is very little warm dust and implying the presence of a large inner hole, at least 31 AU (approx1arc sec) in radius, around the star. The properties of this star-disk system are compared with similar observations of other systems. We also discuss prospects for future observations that may be able to determine whether the inner hole is maintained by the dynamical effect of an unseen orbiting companion.
The Metallicity of the HD 98800 System Laskar, Tanmoy; Soderblom, David R; Valenti, Jeff A ...
The Astrophysical journal,
06/2009, Letnik:
698, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Pre-main-sequence (PMS) binaries and multiples enable critical tests of stellar models if masses, metallicities, and luminosities of the component stars are known. We have analyzed high-resolution, ...high signal-to-noise echelle spectra of the quadruple-star system HD 98800 and using spectrum synthesis computed fits to the composite spectrum for a full range of plausible stellar parameters for the components. We consistently find that subsolar metallicity yields fits with lower xi 2 values, with an overall best fit of M/H = -0.20 - 0.10. This metallicity appears to be consistent with PMS evolutionary tracks for the measured masses and luminosities of the components of HD 98800 but additional constraints on the system and modeling are needed.
Fluxes and upper limits in the wavelength range from 3.6 to 70 mm from the Spitzer Space Telescope are provided for 20 solar-mass Pleiades members. One of these stars shows a probable mid-IR excess, ...and two others have possible excesses, presumably due to circumstellar debris disks. For the star with the largest, most secure excess flux at MIPS (Multiband Imaging Photometer for Spitzer) wavelengths, HII 1101, we derive log(Ldust/L*) ~ -3.8 and an estimated debris disk mass of 4.2 X 10-5 M for an assumed uniform dust grain size of 10 mm. If the stars with detected excesses are interpreted as stars with relatively recent, large collisional events producing a transient excess of small dust particles, the frequency of such disk transients is ~10% for our ~100 Myr, Pleiades G dwarf sample. For the stars without detected 24-70 mm excesses, the upper limits to their fluxes correspond to approximate 3 s upper limits to their disk masses of 6 X 10-6 M using the MIPS 24 mm upper limit or 2 X 10-4 M using the MIPS 70 mm limit. These upper limit disk masses (for 'warm' and 'cold' dust, respectively) are roughly consistent with, but somewhat lower than, predictions of a heuristic model for the evolution of an 'average' solar-mass star's debris disk based on extrapolation backward in time from current properties of the Sun's Kuiper Belt.
How Old Is That Star? Soderblom, David R.
Science (American Association for the Advancement of Science),
01/2009, Letnik:
323, Številka:
5910
Journal Article
Recenzirano
Despite being fundamental in determining its physical state, a star's age cannot be measured directly, and estimation methods are imprecise.
Can observations of Li in F, G, and K stars be used to derive an age for an individual star or a group? This is a brief progress report on using Li for age estimation in PMS and ZAMS stars.
PDF
