Stellar Populations at the Center of IC 1613

We have observed the center of the Local Group dwarf irregular galaxy IC 1613 with WFPC2 aboard the Hubble Space Telescope in the F439W, F555W, and F814W filters. We find a dominant old stellar population (aged ~7 Gyr), identifiable by the strong red giant branch (RGB) and red clump populations. From the (V-I) color of the RGB, we estimate a mean metallicity of the intermediate-age stellar population [Fe/H] = -1.38 +/- 0.31. We confirm a distance of 715 +/- 40 kpc using the I-magnitude of the RGB tip. The main-sequence luminosity function down to I ~25 provides evidence for a roughly constant SFR of approximately 0.00035 solar masses per year across the WFPC2 field of view (0.22 square kpc) during the past 250-350 Myr. Structure in the blue loop luminosity function implies that the SFR was ~50% higher 400-900 Myr ago than today. The mean heavy element abundance of these young stars is 1/10th solar. The best explanation for a red spur on the main-sequence at I = 24.7 is the blue horizontal branch component of a very old stellar population at the center of IC 1613. We have also imaged a broader area of IC 1613 using the 3.5-meter WIYN telescope under excellent seeing conditions. The AGB-star luminosity function is consistent with a period of continuous star formation over at least the age range 2-10 Gyr. We present an approximate age-metallicity relation for IC 1613, which appears similar to that of the Small Magellanic Cloud. We compare the Hess diagram of IC 1613 to similar data for three other Local Group dwarf galaxies, and find that it most closely resembles the nearby, transition-type dwarf galaxy Pegasus (DDO 216).Comment: To appear in the September 1999 Astronomical Journal. LaTeX, uses AASTeX v4.0, emulateapj style file, 19 pages, 12 postscript figures, 2 tables. 5 of the figures available separately via the WW

Hydrothermal circulation within the Endeavour Segment, Juan de Fuca Ridge

Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 11 (2010): Q05002, doi:10.1029/2009GC002957.Areas of the seafloor at mid-ocean ridges where hydrothermal vents discharge are easily recognized by the dramatic biological, physical, and chemical processes that characterize such sites. Locations where seawater flows into the seafloor to recharge hydrothermal cells within the crustal reservoir are by contrast almost invisible but can be indirectly identified by a systematic grid of conductive heat flow measurements. An array of conductive heat flow stations in the Endeavour axial valley of the Juan de Fuca Ridge has identified recharge zones that appear to represent a nested system of fluid circulation paths. At the scale of an axial rift valley, conductive heat flow data indicate a general cross-valley fluid flow, where seawater enters the shallow subsurface crustal reservoir at the eastern wall of the Endeavour axial valley and undergoes a kilometer of horizontal transit beneath the valley floor, finally exiting as warm hydrothermal fluid discharge on the western valley bounding wall. Recharge zones also have been identified as located within an annular ring of very cold seafloor around the large Main Endeavour Hydrothermal Field, with seawater inflow occurring within faults that surround the fluid discharge sites. These conductive heat flow data are consistent with previous models where high-temperature fluid circulation cells beneath large hydrothermal vent fields may be composed of narrow vertical cylinders. Subsurface fluid circulation on the Endeavour Segment occurs at various crustal depths in three distinct modes: (1) general east to west flow across the entire valley floor, (2) in narrow cylinders that penetrate deeply to high-temperature heat sources, and (3) supplying low-temperature diffuse vents where seawater is entrained into the shallow uppermost crust by the adjacent high-temperature cylindrical systems. The systematic array of conductive heat flow measurements over the axial valley floor averaged ∼150 mW/m2, suggesting that only about 3% of the total energy flux of ocean crustal formation is removed by conductive heat transfer, with the remainder being dissipated to overlying seawater by fluid advection.Funding was provided by NSF grants OCE0318566 and OCE0241294 and NSF/SGER grant OCE0902626

Weighing stars from birth to death : mass determination methods across the HRD

Funding: C.A., J.S.G.M., and M.G.P. received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 670519: MAMSIE). N.B. gratefully acknowledge financial support from the Royal Society (University Research Fellowships) and from the European Research Council (ERC-CoG-646928, Multi-Pop).The mass of a star is the most fundamental parameter for its structure, evolution, and final fate. It is particularly important for any kind of stellar archaeology and characterization of exoplanets. There exist a variety of methods in astronomy to estimate or determine it. In this review we present a significant number of such methods, beginning with the most direct and model-independent approach using detached eclipsing binaries. We then move to more indirect and model-dependent methods, such as the quite commonly used isochrone or stellar track fitting. The arrival of quantitative asteroseismology has opened a completely new approach to determine stellar masses and to complement and improve the accuracy of other methods. We include methods for different evolutionary stages, from the pre-main sequence to evolved (super)giants and final remnants. For all methods uncertainties and restrictions will be discussed. We provide lists of altogether more than 200 benchmark stars with relative mass accuracies between [0.3 ,2 ]% for the covered mass range of M ∈[0.1 ,16 ] M⊙ , 75 % of which are stars burning hydrogen in their core and the other 25 % covering all other evolved stages. We close with a recommendation how to combine various methods to arrive at a "mass-ladder" for stars.PostprintPeer reviewe

Weighing stars from birth to death: mass determination methods across the HRD

The mass of a star is the most fundamental parameter for its structure, evolution, and final fate. It is particularly important for any kind of stellar archaeology and characterization of exoplanets. There exists a variety of methods in astronomy to estimate or determine it. In this review we present a significant number of such methods, beginning with the most direct and model-independent approach using detached eclipsing binaries. We then move to more indirect and model-dependent methods, such as the quite commonly used isochrone or stellar track fitting. The arrival of quantitative asteroseismology has opened a completely new approach to determine stellar masses and to complement and improve the accuracy of other methods. We include methods for different evolutionary stages, from the pre-main sequence to evolved (super)giants and final remnants. For all methods uncertainties and restrictions will be discussed. We provide lists of altogether more than 200 benchmark stars with relative mass accuracies between $[0.3,2]\%$ for the covered mass range of M\in [0.1,16]\,\msun, $75\%$ of which are stars burning hydrogen in their core and the other $25\%$ covering all other evolved stages. We close with a recommendation how to combine various methods to arrive at a "mass-ladder" for stars.Comment: Invited review article for The Astronomy and Astrophysics Review. 146 pages, 16 figures, 11 tables. Accepted version by the Journal. It includes summary figure of accuracy/precision of methods for mass ranges and summary table for individual method

Weighing stars from birth to death: mass determination methods across the HRD

The mass of a star is the most fundamental parameter for its structure, evolution, and final fate. It is particularly important for any kind of stellar archaeology and characterization of exoplanets. There exist a variety of methods in astronomy to estimate or determine it. In this review we present a significant number of such methods, beginning with the most direct and model-independent approach using detached eclipsing binaries. We then move to more indirect and model-dependent methods, such as the quite commonly used isochrone or stellar track fitting. The arrival of quantitative asteroseismology has opened a completely new approach to determine stellar masses and to complement and improve the accuracy of other methods. We include methods for different evolutionary stages, from the pre-main sequence to evolved (super)giants and final remnants. For all methods uncertainties and restrictions will be discussed. We provide lists of altogether more than 200 benchmark stars with relative mass accuracies between [0.3,2]% for the covered mass range of M∈[0.1,16]M⊙, 75% of which are stars burning hydrogen in their core and the other 25% covering all other evolved stages. We close with a recommendation how to combine various methods to arrive at a “mass-ladder” for stars.Instituto de Astrofísica de La Plat

Bouchard, Jean-François, Recherches archéologiques dans la région de Tumaco (Colombie).

Tolstoy Paul. Bouchard, Jean-François, Recherches archéologiques dans la région de Tumaco (Colombie).. In: Journal de la Société des Américanistes. Tome 71, 1985. pp. 221-223

Rice, D. S. (ed). —Latin American Horizons. A Symposium at Dumbarton Oaks 11th and 12th October 1986

Tolstoy Paul. Rice, D. S. (ed). —Latin American Horizons. A Symposium at Dumbarton Oaks 11th and 12th October 1986. In: Journal de la Société des Américanistes. Tome 80, 1994. pp. 298-302