Constraints on the height of the inner disk rim in pre-main-sequence stars

The structure of inner region of protoplanetary disks around young pre-main-sequence stars is still poorly understood. This part of the disk is shaped by various forces that influence dust and gas dynamics, and by dust sublimation, which creates abrupt drops in the dust density. This region also emits strong near-infrared excess that cannot be explained by classical accretion disk models, which suggests the existence of some unusual dust distribution or disk shape. The most prevalent explanation to date is the puffed-up inner disk rim model, where the disk exhibits an optically thin cavity around the star up to the distance of dust sublimation. The critical parameter in this model is the inner disk rim height $z_{\rm max}$ relative to the rim distance from the star $R_{\rm in}$. Observations often require $z_{\rm max}/R_{\rm in}\gtrsim0.2$ to reproduce the near-infrared excess in the spectra. We compile a comprehensive list of processes that can shape the inner disk rim and combine them into a self-consistent model. Two of them, radiation pressure force and the gas velocity profile, have never been applied in this context before. The aim was to find the most plausible theoretical values of $z_{\rm max}/R_{\rm in}$. The results show that this value is $\lesssim$0.13 for Herbig Ae stars, $\lesssim$0.11 for T Tau stars, and $\lesssim$0.10 for young brown dwarfs. This is lower than the observational requirements for Herbig Ae stars. We argue that the same problem exists in T Tau stars as well. We conclude that the puffed-up inner rim model cannot be the sole explanation for the near-infrared excess in young pre-main-sequence stars.Comment: Research Note, accepted in Astronomy and Astrophysic

Temperature inversion on the surface of externally heated optically thick multigrain dust clouds

It was recently discovered that the temperature in the surface layer of externally heated optically thick gray dust clouds increases with the optical depth for some distance from the surface, as opposed to the normal decrease in temperature with distance in the rest of the cloud. This temperature inversion is a result of efficient absorption of diffuse flux from the cloud interior by the surface dust exposed to the external radiation. A micron or bigger size grains experience this effect when the external flux is of stellar spectrum. We explore what happens to the effect when dust is a mixture of grain sizes (multigrain). Two possible boundary conditions are considered: i) a constant external flux without constrains on the dust temperature, and ii) the maximum dust temperature set to the sublimation temperature. We find that the first condition allows small grains to completely suppress the temperature inversion of big grains if the overall opacity is dominated by small grains. The second condition enables big grains to maintain the inversion even when they are a minor contributor to the opacity. In reality, the choice of boundary condition depends on the dust dynamics. When applied to the physics of protoplanetary disks, the temperature inversion leads to a previously unrecognized disk structure where optically thin dust can exist inside the dust destruction radius of an optically thick disk. We conclude that the transition between the dusty disk and the gaseous inner clearing is not a sharp edge, but rather a large optically thin region.Comment: 8 pages, 10 figures, Accepted for publication in the Astrophysical Journa

Obrazovne asimetrije u nastajanju: natjecanja učenika kao indikatori ekonomskog razvoja

Croatia does not score well in the human development index, rate of employment, or development of the high tech sector – to mention only a few indicators that hinder good prospects for improvement. Also, Croatian high school students are at the bottom of European rankings on performance in science and mathematics and their interest in career in science is declining. Croatia needs more educated people, especially in the area of science and technology, and this can be achieved only if the youth become interested in science at an early age. Thus, science fair competitions are of an utmost importance for development of Croatia. This paper aims at investigating a relation of the Croatian counties’ development index and their students’ participation rates in the science fair competitions. This is done by including two development indexes in search for the relation with the counties’ participation rates in biology, chemistry, physics and mathematics competition, and with a reference to a previous research on astronomy competition. As is revealed, there is a growing trend of interconnection of the development index and participation rates at science competitions in all disciplines.Hrvatska ne stoji dobro na ljestvici indeksa razvijenosti, stope zaposlenosti, razvoja visokotehnološkog sektora, što su samo neki od indikatora koji ne daju perspektivu promjene na bolje. Također, hrvatski srednjoškolci su na dnu ljestvice u Europi po rezultatima na testovima znanosti, a opada i njihov interes za karijeru u znanosti. Hrvatska treba više obrazovanih ljudi, posebice u području znanosti i tehnologije, što se može postići jedino ukoliko se mlade u najranijoj dobi zainteresira za znanost. Stoga su natjecanja u pojedinim znanstvenim disciplinama od presudne važnosti za razvoj Hrvatske. Ovaj članak cilja ka istraživanju povezanosti indeksa razvijenosti županija sa stopom sudjelovanja učenika na natjecanjima. Navedeno će se postići uključenjem dvaju indeksa razvijenosti u traženje povezanosti sa stopama sudjelovanja u natjecanjima iz biologije, kemije, fizike i matematike, uz pregled prethodnog istraživanja za natjecanje iz astronomije. Kao što će se pokazati, postoji rastući trend međusobne povezanosti indeksa razvijenosti i stopa sudjelovanja učenika na natjecanjima po svim disciplinama

Dust Emission from Herbig AE/BE Stars: Evidence for Disks and Envelopes

Infrared and millimeter-wave emission from Herbig Ae/Be stars has produced conflicting conclusions regarding the dust geometry in these objects. We show that the compact dimensions of the millimeter-wave-emitting regions are a decisive indication for disks. But a disk cannot explain the spectral energy distribution unless it is embedded in an extended envelope that (1) dominates the IR emission and (2) provides additional disk heating on top of the direct stellar radiation. Detailed radiative transfer calculations based on the simplest model for envelope-embedded disks successfully fit the data from UV to millimeter wavelengths and show that the disks have central holes. This model also resolves naturally some puzzling results of IR imaging

Dust Emission from Herbig Ae/Be stars - Evidence for Disks and Envelopes

IR and mm-wave emission from Herbig Ae/Be stars has produced conflicting conclusions regarding the dust geometry in these objects. We show that the compact dimensions of the mm-wave emitting regions are a decisive indication for disks. But a disk cannot explain the spectral energy distribution (SED) unless it is embedded in an extended envelope that (1) dominates the IR emission and (2) provides additional disk heating on top of the direct stellar radiation. Detailed radiative transfer calculations based on the simplest model for envelope-embedded disks successfully fit the data from UV to mm wavelengths and show that the disks have central holes. This model also resolves naturally some puzzling results of IR imaging.Comment: 9 pages, 2 figures. accepted to ApJ

Luminosity indicators in dusty photoionized environments

The luminosity of the central source in ionizing radiation is an essential parameter in a photoionized environment, and one of the most fundamental physical quantities one can measure. We outline a method of determining luminosity for any emission-line region using only infrared data. In dusty environments, grains compete with hydrogen in absorbing continuum radiation. Grains produce infrared emission, and hydrogen produces recombination lines. We have computed a very large variety of photoionization models, using ranges of abundances, grain mixtures, ionizing continua, densities, and ionization parameters. The conditions were appropriate for such diverse objects as H II regions, planetary nebulae, starburst galaxies, and the narrow and broad line regions of active nuclei. The ratio of the total thermal grain emission relative to H$\beta$ (IR/H$\beta$) is the primary indicator of whether the cloud behaves as a classical Str\"{o}mgren sphere (a hydrogen-bounded nebula) or whether grains absorb most of the incident continuum (a dust-bounded nebula). We find two global limits: when $IR/H\beta<100$ infrared recombination lines determine the source luminosity in ionizing photons; when $IR/H\beta\gg100$ the grains act as a bolometer to measure the luminosity.Comment: 12 pages 3 figures. Accepted ASP Sept.9

Uvođenje autohtonih ekotipova češnjaka in vitro pod utjecajem regulatora rasta i svjetlost

Garlic is valuable crop that is used not only for human consumption, but also in pharmaceutical, food and cosmetics industries. Indigenous cultivars have specific beneficial properties that could be permanently lost due to cultivation of new cultivars. Aim of this study was to established two indigenous garlic cultivars in vitro under influence of growth regulator and light. Garlic varieties Slavonian winter (Croatia) and Vincek (Slovenia) were introduced on medium supplemented with two different concentrations of BAP (1 and 1,5 mg/L) and grown under two types of light (FLUO and LED). Results showed there were no significant influence of light type but concentration of growth regulator significantly influenced in vitro development of garlic microshoots of both investigated cultivars. The best treatment for Vincek garlic explants was nutrient medium supplemented with 1.5 mg/L BAP and LED lights, while for Slavonian winter garlic the best treatment showed to be FLUO light and 1,5 mg/L BAP.Češnjak je dragocjena kultura koja se koristi osim za ljudsku prehranu, i u farmaceutskoj, prehrambenoj i kozmetičkoj industriji. Autohtone sorte imaju specifična korisna svojstva koja bi mogla biti trajno izgubljena uzgojem novih kultivara. Cilj ovog istraživanja bio je uspostaviti in vitro protokol za uzgoj dvije autohtone sorte češnjaka pod utjecajem regulatora rasta i svjetla. U in vitro kulturu uvedene su autohtone sorte češnjaka Slavonski ozimi (Hrvatska) i Vincek (Slovenija) na dvije različite varijante hranjive podloge (1 i 1,5 mg/L BAP-a) te su uzgajane pod dvije varijante osvjetljenja (FLUO i LED). Rezultati su pokazali da nije bilo značajnog utjecaja vrste svjetla, ali je koncentracija regulatora rasta značajno utjecala na in vitro razvoj mikroizdanaka češnjaka obje ispitivane sorte. Eksplantati češnjaka Vincek postigli su bolje rezultate na tretmanu hranjive podloge s dodatkom 1,5 mg/L BAP-a i LED svjetla, dok se za Slavonski ozimi češnjak pokazao najbolji tretman FLUO svjetlo i 1,5 mg/L BAP-a

ANTIOKSIDATIVNI ODGOVOR U LISTU JAGODA (Fragaria x ananassa Duch) NA TRETMANE BIOSTIMULATORIMA UZ REDUCIRANU GNOJIDBU DUŠIKOM I KALIJEM

Strawberry cultivar Elsanta was grown in peat based substrate in a green house. Full dose and 50% reduced nitrogen and potassium fertilization were applied during fruit bearing period in spring, along with biostimulators Viva®, Megafol® and their combination. The specific activities of guaiacol peroxidase (GPXs; EC 1.11.1.7), catalase (CATs; EC 1.11.1.6), ascorbate peroxidase (APXs; EC 1.11.1.11) and glutathione reductase (GRs; EC 1.6.4.2) in strawberry leaf were stimulated by biostimulators and reduced fertilization. The strongest link seen here was between the enzymes of ascorbate-glutathione cycle (APXs and GRs), which were positively related to trifoliate leaf fresh mass (TLFM). The highest TLFM was observed in Megafol® treated plants.Sorta jagoda Elsanta uzgajana je u tresetnom supstratu u plasteniku. Puna doza i 50% smanjena doza dušika i kalija primjenjene su tijekom proljetnoga plodonošenja, uz primjenu biostimulatora Viva®, Megafol® i njihove kombinacije. Specifične aktivnosti gvajakol peroksidaze (GPXs; EC 1.11.1.7), katalaze (CATs; EC 1.11.1.6), askorbat peroksidaze (APXs; EC 1.11.1.11) i glutation reduktaze (GRs; EC 1.6.4.2) u listu jagode bile su značajno više poslije tretiranja biostimulatorima i reduciranom gnojidbom. Najjača povezanost uočena u ovom istraživanju, bila je između enzima askorbat-glutation ciklusa (APXs i GRs), koji su bili u pozitivnoj korelaciji s masom svježega lista (TLFM). Najveća masa svježega lista (TLFM) uočena je na biljkama tretiranim Megafolom®