Using Narrow Band Photometry to Detect Young Brown Dwarfs in IC348

We report the discovery of a population of young brown dwarf candidates in the open star cluster IC348 and the development of a new spectroscopic classification technique using narrow band photometry. Observations were made using FLITECAM, the First Light Camera for SOFIA, at the 3-m Shane Telescope at Lick Observatory. FLITECAM is a new 1-5 micron camera with an 8 arcmin field of view. Custom narrow band filters were developed to detect absorption features of water vapor (at 1.495 microns) and methane (at 1.66 microns) characteristic of brown dwarfs. These filters enable spectral classification of stars and brown dwarfs without spectroscopy. FLITECAM's narrow and broadband photometry was verified by examining the color-color and color-magnitude characteristics of stars whose spectral type and reddening was known from previous surveys. Using our narrow band filter photometry method, it was possible to identify an object measured with a signal-to-noise ratio of 20 or better to within +/-3 spectral class subtypes for late-type stars. With this technique, very deep images of the central region of IC348 (H ~ 20.0) have identified 18 sources as possible L or T dwarf candidates. Out of these 18, we expect that between 3 - 6 of these objects are statistically likely to be background stars, with the remainder being true low-mass members of the cluster. If confirmed as cluster members then these are very low-mass objects (~5 Mjupiter). We also describe how two additional narrow band filters can improve the contrast between M, L, and T dwarfs as well as provide a means to determine the reddening of an individual object.Comment: 43 pages, 17 figures. Accepted for publication in the Astrophysical Journal 27 June 200

Spectropolarimetry of the H-alpha line in Herbig Ae/Be stars

Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS telescope, we have obtained a large number of high precision spectropolarimetrc observations (284) of Herbig AeBe stars collected over 53 nights totaling more than 300 hours of observing. Our sample of five HAeBe stars: AB Aurigae, MWC480, MWC120, MWC158 and HD58647, all show systematic variations in the linear polarization amplitude and direction as a function of time and wavelength near the H-alpha line. In all our stars, the H-alpha line profiles show evidence of an intervening disk or outflowing wind, evidenced by strong emission with an absorptive component. The linear polarization varies by 0.2% to 1.5% with the change typically centered in the absorptive part of the line profile. These observations are inconsistent with a simple disk-scattering model or a depolarization model which produce polarization changes centered on the emmissive core. We speculate that polarized absorption via optical pumping of the intervening gas may be the cause.Comment: Accepted for publication in ApJ Letter

Identifying Young Brown Dwarfs Using Gravity-Sensitive Spectral Features

We report the initial results of the Brown Dwarf Spectroscopic Survey Gravity Project, to study gravity sensitive features as indicators of youth in brown dwarfs. Low-resolution (R~2000) J-band and optical (R~1000) observations using NIRSPEC and LRIS at the W.M. Keck Observatory reveal transitions of TiO, VO, K I, Na I, Cs I, Rb I, CaH, and FeH. By comparing these features in late-type giants and in old field dwarfs we show that they are sensitive to the gravity (g = GM/R^2) of the object. Using low-gravity spectral signatures as age indicators, we observed and analyzed J-band and optical spectra of two young brown dwarfs, G 196-3B (20-300 Myr) and KPNO Tau-4 (1-2 Myr), and two possible low mass brown dwarfs in the sigma Orionis cluster (3-7 Myr). We report the identification of the phi bands of TiO near 1.24 microns and the A-X band of VO near 1.18 microns together with extremely weak J-band lines of K I in KPNO-Tau4. This is the first detection of TiO and VO in the J-band in a sub-stellar mass object. The optical spectrum of KPNO-Tau4 exhibits weak K I and Na I lines, weak absorption by CaH, and strong VO bands, also signatures of a lower gravity atmosphere. G 196-3B shows absorption features in both wavelength regions like those of KPNO-Tau4 suggesting that its age and mass are at the lower end of published estimates. Whereas sigma Ori 51 appears to be consistent with a young sub-stellar object, sigma Ori 47 shows signatures of high gravity most closely resembling an old L1.5/L0, and can not be a member of the sigma Orionis cluster.Comment: 14 pages, 4 figures. To appear in the January 10, 2004 issue of the Astrophysical Journa

ISTRAŽIVANJE MOGUĆNOSTI RASTA KOMARČI DRŽANIH U KOMERCIJALNOM RECIRKULACIJSKOM SISTEMU I TRETIRANIH NUSPROIZVODOM INDUSTRIJSKE PROIZVODNJE GOVEĐEG HORMONA RASTA

Gilthead sea bream, maintained in a commercial scale recirculation system, were subjected to three injections (0,5 and 10 µg -1 body weight) with a by-product from the industrial production of recombinant bovine growth hormone (rbGH). Injections were provided at experiment start and at 3 and 6 weeks. Growth performance of animals was evaluated over a period of 8 weeks (n = 171 per treatment). At trial end fish were examined for proximate composition, fillet yield and visceral indices. No differences were recorded in individual growth performance between the three treatment groups (P > 0.05). Examination of protein productive value and protein efficiency ratio indicated approximately 20% of dietary protein was incorporated into animals irrespective of treatment. However incorporation of dietary lipid decreased with increasing dose of rbGH. High dose GH decreased liver weight (P 0,05). Istraživanje vrijednosti produktivnog proteina i količine efikasnosti proteina pokazalo je da je približno 20% proteina bilo inkorporirano u životinje neovisno o tretmanu. No inkorporacija lipida bila je smanjena povećanjem doze hormona rasta (rbGH). Visoka doza hormona rasta smanjila je težinu jetre (P < 0,05) u usporedbi s kontrolom s istodobnim smanjenjem hepatosomatskog indeksa (P < 0,05). Težina i postotak fileta bili su viši u životinja tretiranih dozom od 10 µg g -1 tjelesne težine u usporedbi s niskom dozom rbGH tretiranih riba (P < 0,05)

ISTRAŽIVANJE MOGUĆNOSTI RASTA KOMARČI DRŽANIH U KOMERCIJALNOM RECIRKULACIJSKOM SISTEMU I TRETIRANIH NUSPROIZVODOM INDUSTRIJSKE PROIZVODNJE GOVEĐEG HORMONA RASTA

Gilthead sea bream, maintained in a commercial scale recirculation system, were subjected to three injections (0,5 and 10 µg -1 body weight) with a by-product from the industrial production of recombinant bovine growth hormone (rbGH). Injections were provided at experiment start and at 3 and 6 weeks. Growth performance of animals was evaluated over a period of 8 weeks (n = 171 per treatment). At trial end fish were examined for proximate composition, fillet yield and visceral indices. No differences were recorded in individual growth performance between the three treatment groups (P > 0.05). Examination of protein productive value and protein efficiency ratio indicated approximately 20% of dietary protein was incorporated into animals irrespective of treatment. However incorporation of dietary lipid decreased with increasing dose of rbGH. High dose GH decreased liver weight (P 0,05). Istraživanje vrijednosti produktivnog proteina i količine efikasnosti proteina pokazalo je da je približno 20% proteina bilo inkorporirano u životinje neovisno o tretmanu. No inkorporacija lipida bila je smanjena povećanjem doze hormona rasta (rbGH). Visoka doza hormona rasta smanjila je težinu jetre (P < 0,05) u usporedbi s kontrolom s istodobnim smanjenjem hepatosomatskog indeksa (P < 0,05). Težina i postotak fileta bili su viši u životinja tretiranih dozom od 10 µg g -1 tjelesne težine u usporedbi s niskom dozom rbGH tretiranih riba (P < 0,05)

Detecting Planets Around Very Low Mass Stars with the Radial Velocity Method

The detection of planets around very low-mass stars with the radial velocity method is hampered by the fact that these stars are very faint at optical wavelengths where the most high-precision spectrometers operate. We investigate the precision that can be achieved in radial velocity measurements of low mass stars in the near infrared (nIR) Y-, J-, and H-bands, and we compare it to the precision achievable in the optical. For early-M stars, radial velocity measurements in the nIR offer no or only marginal advantage in comparison to optical measurements. Although they emit more flux in the nIR, the richness of spectral features in the optical outweighs the flux difference. We find that nIR measurement can be as precise than optical measurements in stars of spectral type ~M4, and from there the nIR gains in precision towards cooler objects. We studied potential calibration strategies in the nIR finding that a stable spectrograph with a ThAr calibration can offer enough wavelength stability for m/s precision. Furthermore, we simulate the wavelength-dependent influence of activity (cool spots) on radial velocity measurements from optical to nIR wavelengths. Our spot simulations reveal that the radial velocity jitter does not decrease as dramatically towards longer wavelengths as often thought. The jitter strongly depends on the details of the spots, i.e., on spot temperature and the spectral appearance of the spot. Forthcoming nIR spectrographs will allow the search for planets with a particular advantage in mid- and late-M stars. Activity will remain an issue, but simultaneous observations at optical and nIR wavelengths can provide strong constraints on spot properties in active stars.Comment: accepted by ApJ, v2 accepted revision with new precision calculations, abstract abride

EGZOENCIMI U HRANI ZA RIBE S POSEBNIM OSVRTOM NA FITAZU: PREGLED

The global aquaculture industry has come under increasing pressure to optimize production efficiency while reducing environmental loadings. These new demands, which have been accompanied in certain countries by legislation, have stimulated the development of elite low output dietary formulations. Several feed manufacturers have developed diets with modified energy: protein ratios, which reduce environmental phosphorus loadings with minimum impact upon fish growth. However, problems relating to end product quality have materialized following application of these high lipid diets and it is clear that alternative strategies must be developed. In particular, there remains an urgent need to replace the expensive fishmeal component of aquafeeds. One approach might be to supplement diets with exogenous enzymes (exoenzymes) that enhance the value and utility of alternative, low grade proteins while reducing ecological impacts. This paper briefly reviews the literature relating to experimental exoenzyme aquafeeds, with specific reference to phytase.Kompletna industrija akvakulture nalazi se pod povećanim pritiskom glede optimalizacije efikasne proizvodnje, dok se u isto vrijeme smanjuju mogućnosti iskorištavanja akvatorija. Ovi, novi zahtjevi koji su u nekim zemljama povezani s legislativom, potaknuli su razvoj niskih iskorištenosti hranidbenih formulacija. Nekoliko proizvođaća razvilo je hrane s modificiranom energijom: količina bjelančevina koja smanjuje nakupljanje P a okolišu s minimalnim utjecajem na rast riba. No, problemi koji se odnose na kvalitetu gotovoga proizvoda materijalirizirani su uporabom hrana s visokim postotkom lipida i jasno je da mora biti razvijena alternativna strategija, napose stoga što ostaje urgentna potreba za zamjenu skupog ribljeg brašna kao komponente u hrani za ribe. Jedna od mogućnosti mogla bi biti dodatak egzogenih enzima (egzoenzima) koji povećavaju vrijednost i iskorištenost nisko vrijednih bjelančevina. U ovom je radu dan kratak prikaz literaturnih podataka koji se odnose na eksperimentalne hrane s egzoenzimima, s posebnim osvrtom na fitazu