We describe future steps in the direct characterization of habitable exoplanets subsequent to medium and large mission projects currently underway and investigate the benefits of spectroscopic and ...direct imaging approaches. We show that, after third- and fourth-generation missions have been conducted over the course of the next 100 years, a significant amount of time will lapse before we will have the capability to observe directly the morphology of extrasolar organisms.
We present HST observations of the lower main sequence of the Galactic globular cluster M3. Our data, obtained with WFPC2 in the F814W and F555W filters, sample a region centred about 4 arcmin away ...from the cluster centre (at ∼4.2 core radii). The photometry of the WF2, WF3 and WF4 fields extends down to V∼26.5 (I∼25), much deeper than any previous ground-based study on this cluster. The resulting luminosity function (LF) for the main sequence covers the interval MI = 3–10.5, and reaches a maximum between MI = 8.5 and 9, sharing in this feature the same behaviour as other clusters studied with HST so far. Making use of four different mass-luminosity (M–L) relations (theoretical and semi-empirical) a present-day mass function (MF) has also been obtained, which spans the mass interval ≃0.8–0.18 M⊙. Independent of the adopted M–L relation, the MF clearly flattens out at the low-mass limits. However, no attempt has been made to take into account possible effects due, for instance, to mass segregation and evaporation.
We analyze the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at z ~ or = 1-3 selected using the Hubble Space Telescope (HST)Wide Field Camera 3 (WFC3) UVIS channel filters. ...These HST/WFC3 observations cover about 50 arcmin2 in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z ~ or = 1-3 are selected using dropout selection criteria similar to high-redshift LBGs. The star-forming galaxies selected using other color-based techniques show similar correlations at z ~ or = 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z ~ or = 2 is essential. The future HST UV surveys, both wider and deeper, covering a large luminosity range are important to better understand LBG properties and their evolution.
The VLTI - A Status Report Glindemann, A; Algomedo, J; Amestica, R ...
Astrophysics and space science,
01/2003, Volume:
286, Issue:
1-2
Journal Article
Peer reviewed
The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approaching completion. After the four 8-m Unit Telescopes (UT) individually saw first light in the last ...years, two of them were combined for the first time on October 30, 2001 to form a stellar interferometer, the VLT Interferometer. The combination in pairs of all four UTs was completed in September 2002. In this article, we will describe the subsystems of the VLTI and the planning for the following years.
A region 23 x 36 arcsec in size centered on the symbiotic Mira RX Pup was imaged for evidence of extended optical emission similar to R Aqr. A bright, one-sided jetlike emission feature easily ...observable in both H-alpha and forbidden N II is found to extend from at least 1.5 to 3.7 arcsec projected distance from the center of the star along the p.a. 15 deg axis. This jet is coaligned with the semimajor axis of the extended 6 cm radio emission nebula recently observed in the inner circumstellar region of RX Pup. The observed forbidden N II/H-alpha ratio is consistent with the emission being due to a plasma photoionized by a hot white dwarf or subdwarf companion. Such a long thin extended feature implies the existence of a very effective mass collimation mechanism possibly associated with a dense equatorial disk. 19 refs.
The discovery of extrasolar planets is one of the greatest achievements of modern astronomy. The detection of planets that vary widely in mass demonstrates that extrasolar planets of low mass exist. ...In this paper, we describe a mission, called Darwin, whose primary goal is the search for, and characterization of, terrestrial extrasolar planets and the search for life. Accomplishing the mission objectives will require collaborative science across disciplines, including astrophysics, planetary sciences, chemistry, and microbiology. Darwin is designed to detect rocky planets similar to Earth and perform spectroscopic analysis at mid-infrared wavelengths (6-20 mum), where an advantageous contrast ratio between star and planet occurs. The baseline mission is projected to last 5 years and consists of approximately 200 individual target stars. Among these, 25-50 planetary systems can be studied spectroscopically, which will include the search for gases such as CO(2), H(2)O, CH(4), and O(3). Many of the key technologies required for the construction of Darwin have already been demonstrated, and the remainder are estimated to be mature in the near future. Darwin is a mission that will ignite intense interest in both the research community and the wider public.
After Earth's origin, our host star, the Sun, was shining 20-25% less brightly than today. Without greenhouse-like conditions to warm the atmosphere, our early planet would have been an ice ball, and ...life may never have evolved. But life did evolve, which indicates that greenhouse gases must have been present on early Earth to warm the planet. Evidence from the geological record indicates an abundance of the greenhouse gas CO(2). CH(4) was probably present as well; and, in this regard, methanogenic bacteria, which belong to a diverse group of anaerobic prokaryotes that ferment CO(2) plus H(2) to CH(4), may have contributed to modification of the early atmosphere. Molecular oxygen was not present, as is indicated by the study of rocks from that era, which contain iron carbonate rather than iron oxide. Multicellular organisms originated as cells within colonies that became increasingly specialized. The development of photosynthesis allowed the Sun's energy to be harvested directly by life-forms. The resultant oxygen accumulated in the atmosphere and formed the ozone layer in the upper atmosphere. Aided by the absorption of harmful UV radiation in the ozone layer, life colonized Earth's surface. Our own planet is a very good example of how life-forms modified the atmosphere over the planets' lifetime. We show that these facts have to be taken into account when we discover and characterize atmospheres of Earth-like exoplanets. If life has originated and evolved on a planet, then it should be expected that a strong co-evolution occurred between life and the atmosphere, the result of which is the planet's climate.
Two sets of ultraviolet images of the Jovian north aurora were obtained with the Faint Object Camera on board the Hubble Space Telescope. The first series shows an intense discrete arc in near ...corotation with the planet. The maximum apparent molecular hydrogen emission rate corresponds to an electron precipitation of ∼1 watt per square meter, which is about 30,000 times larger than the solar heating by extreme ultraviolet radiation. Such a particle heating rate of the auroral upper atmosphere of Jupiter should cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours after initial observation, the discrete arc had decreased in brightness by more than one order of magnitude. The time scale and magnitude of the change in the ultraviolet aurora leads us to suggest that the discrete Jovian auroral precipitation is related to large-scale variations in the current system, as is the case for Earth's discrete aurorae.
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