Optimal slit orientation for long multi-object spectroscopic exposures

Historically, long-slit spectroscopic observations were carried out using the parallactic angle for the slit orientation if slit loss was an important consideration (either to maximize the signal-to-noise or to do spectrophotometry). This requires periodic realignment of the slit position angle as the parallactic angle changes. This is not possible for multi-slit observations where one slit position angle must be chosen for the entire exposure. Common wisdom suggests using the parallactic angle at the meridian (HA=0). In this paper, I examine what the best strategy is for long, multi-slit exposures. I find that in extreme cases (very long exposure time) the best choice is to orient the slit \emph{perpendicular} to the parallactic angle at the meridian. There are two effects to consider: the increasing dispersion with increasing airmass and the changing angle between the parallactic angle and the slit. In the case of \emph{traditional} slit orientation, the two effects amplify each other, thus rendering a significant fraction of the observation useless. Using the perpendicular orientation, the two processes work against each other, thus most of the observation remains useful. I will use, as an example, our 8 hour Lockman Hole observations using the Keck telescope, but generic methods are given to evaluate a particular observation. I also make the tools available to the community.Comment: Accepted by A&A (20/06/2005

Simultaneous Multicolor Detection of Faint Galaxies in the Hubble Deep Field

We present a novel way to detect objects when multiband images are available. Typically, object detection is performed in one of the available bands or on a somewhat arbitrarily co-added image. Our technique provides an almost optimal way to use all the color information available. We build up a composite image of the N passbands where each pixel value corresponds to the probability that the given pixel is just sky. By knowing the probability distribution of sky pixels (a chi-square distribution with N degrees of freedom), the data can be used to derive the distribution of pixels dominated by object flux. From the two distributions an optimal segmentation threshold can be determined. Clipping the probability image at this threshold yields a mask, where pixels unlikely to be sky are tagged. After using a standard connected-pixel criterion, the regions of this mask define the detected objects. Applying this technique to the Hubble Deep Field data, we find that we can extend the detection limit of the data below that possible using linearly co-added images. We also discuss possible ways of enhancing object detection probabilities for certain well defined classes of objects by using various optimized linear combinations of the pixel fluxes (optimal subspace filtering).Comment: 8 pages, 5 figures (4 postscript, 1 JPEG). To be published in A

Az élethosszig tartó tanulás kihívásai: középpontban a tanuló szervezet

Margaret Mead 1960 körül a kultúrák válfajait úgy különböztette meg, hogy van „a posztfiguratív kultúra, amelyben a gyerekek elsősorban elődeiktől tanulnak, a konfiguratív kultúra, amelyben mind a gyerekek, mind a felnőttek a velük egykorúaktól és egyenrangúaktól tanulnak és a prefiguratív kultúra, amelyben a felnőttek gyerekeiktől is tanulnak …” (Nyíri, 2009

Correcting second-order contamination in low-resolution spectra

An empirical method for correcting low-resolution astronomical spectra for second-order contamination is presented. The method was developed for correcting spectra obtained with grism #4 of the ALFOSC spectrograph at the Nordic Optical Telescope and the performance is demonstrated on spectra of two nearby bright Type Ia supernovae.Comment: accepted for publication in Astronomical Notes (Astronomische Nachrichten

A Puzzling X-Ray Source Found in the chandra Deep Field South

In this letter we report the detection of an extremely strong X-ray emission line in the 940ks chandra ACIS-I spectrum of CXO CDFS J033225.3-274219. The source was identified as a Type1 AGN at redshift of z = 1.617, with 2.0 -- 10.0 keV rest frame X-ray luminosity of ~ 10^44 ergs s^-1. The emission line was detected at 6.2^{+0.2}_{-0.1} keV, with an equivalent width (EW) of 4.4^{+3.2}_{-1.4} keV, both quantities referring to the observed frame. In the rest frame, the line is at 16.2^{+0.4}_{-0.3} keV with an EW of 11.5^{+8.3}_{-3.7} keV. An X-ray emission line at similar energy (~ 17 keV, rest frame) in QSO PKS 2149-306 was discovered before using ASCA data. We reject the possibility that the line is due to a statistical or instrumental artifact. The line is most likely due to blueshifted Fe-K emission from an relativistic outflow, probably an inner X-ray jet, with velocities of the order of ~ 0.6-0.7c. Other possible explanations are also discussed

The Near-Infrared Number Counts and Luminosity Functions of Local Galaxies

This study presents a wide-field near-infrared (K-band) survey in two fields; SA 68 and Lynx 2. The survey covers an area of 0.6 deg.$^2$, complete to K=16.5. A total of 867 galaxies are detected in this survey of which 175 have available redshifts. The near-infrared number counts to K=16.5 mag. are estimated from the complete photometric survey and are found to be in close agreement with other available studies. The sample is corrected for incompleteness in redshift space, using selection function in the form of a Fermi-Dirac distribution. This is then used to estimate the local near-infrared luminosity function of galaxies. A Schechter fit to the infrared data gives: M$^\ast_K = -25.1 \pm 0.3$, $\alpha = -1.3\pm 0.2$ and $\phi^\ast =(1.5\pm 0.5)\times 10^{-3}$ Mpc$^{-3}$ (for H$_0=50$ Km/sec/Mpc and q$_0=0.5$). When reduced to $\alpha=-1$, this agrees with other available estimates of the local IRLF. We find a steeper slope for the faint-end of the infrared luminosity function when compared to previous studies. This is interpreted as due to the presence of a population of faint but evolved (metal rich) galaxies in the local Universe. However, it is not from the same population as the faint blue galaxies found in the optical surveys. The characteristic magnitude ($M^\ast_K$) of the local IRLF indicates that the bright red galaxies ($M_K\sim -27$ mag.) have a space density of $\le 5\times 10^{-5}$ Mpc$^{-3}$ and hence, are not likely to be local objects.Comment: 24 pages, 8 figures, AASTEX 4.0, published in ApJ 492, 45

The bright optical/NIR afterglow of the faint GRB 080710 - Evidence for a jet viewed off axis

We investigate the optical/near-infrared light curve of the afterglow of GRB 080710 in the context of rising afterglows. Optical and near-infrared photometry was performed using the seven channel imager GROND and the Tautenburg Schmidt telescope. X-ray data were provided by the X-ray Telescope onboard the Swift satellite. The optical/NIR light curve of the afterglow of GRB 080710 is dominated by an initial increase in brightness, which smoothly turns over into a shallow power law decay. The initially rising achromatic light curve of the afterglow of GRB 080710 can be accounted for with a model of a burst viewed off-axis or a single jet in its pre deceleration phase and in an on-axis geometry. An unified picture of the afterglow light curve and prompt emission properties can be obtained with an off-axis geometry, suggesting that late and shallow rising optical light curves of GRB afterglows might be produced by geometric effects.Comment: 9 pages, 4 figures, accepted by A and

A nemi különbségek és az életkor hatása az immunreaktivitásra a szervezetet ért sérülések után = Effect of age and the sexual differences on the immuno-reactivity following injury

A nemi különbségek és az életkor hatása az immunreaktivitásra a szervezetet ért sérülések után. A kutatásokban a vázizom iszkémia-reperfúzió hatását vizsgáltuk az immunsejtek funkcióváltozásaira és az oxidatív stressz paramétereire mind humán, mind állatkíséreltekben. Fontosabb kutatási eredmények: Az állatkísérletekben az egyes kísérleti csoportok között nem volt különbség a granulocyta funkciókat illetően sem az életkor sem pedig a nem tekintetében. A lipid peroxidáció mértéke nőstény állatokban fokozottabb volt, ugyanakkor az antioxidáns kapacitás is nagyobb volt a reperfúzió során. Az iszkémiás prekondícionálás nemtől és kortól függetlenül fokozta a plazma antioxidáns kapacitását a reperfúzió kezdetén és 24 óra után is. A humán mérésekben a granulocyta-thrombocyta komplexek száma csökken a reperfúzió kezdetén és függ az iszkémia időtartamától, ugyanakkor a thrombocyta aggregáció nem változott. Az oxidatív stressz paramétere nem változott a reperfúzió során, ugyanakkor az antioxidáns kapacitás a plazmában csökkent. Következtetések: A speciálisan kezelt (kasztrált, hormonkezelt) állatoknál lehet nemtől függő különbség a gyulladásos válaszban, de ezt a normál populáción végzett mérések nem igazolták. A humán mérések megerősítették az oxidatív stressz fontos szerepét az izom reperfúziós károsodásával járó állapotokban, bár ezt a védekező mechanizmusok kompenzálni képesek. | Role of age and gender differences on the immunoreactivity after injuries of the body. Effect of ischemia-reperfusion of the skeletal muscle on the immune cell functions and on the oxidative stress was investigated in animal and human studies. Main results: In the animal studies there were no major differences among the different experimental groups concerning gender and age differences. The extent of lipid peroxidation was higher in female animals, however, antioxidant capacity was also higher during reperfusion. Ischemic preconditioning increased plasma antioxidant capacity at early reperfusion and 24 hours later. In human studies the number of granulocyte-thrombocyte complexes decreased during early reperfusion and they were indirectly proportional with the duration of ischemia. Aggregation of thrombocytes did not change. Parameters of oxidative stress did not change during reperfusion and but antioxidant capacity decreased in plasma. No gender differences were seen in these parameters. Conclusions: In specially composed experimental conditions (castration, hormone treatment) there might be differences in various biological parameters, however, our studies carried out on normal populations, do not support this theory. Our human studies support the role of oxidative stress in muscle reperfusion injury, however, antioxidant mechanisms can compensate these changes