Predictions of variable mass loss for Luminous Blue Variables

We present radiation-driven wind models for Luminous Blue Variables (LBVs) and predict their mass-loss rates. We study the effects of lower masses and modified abundances in comparison to the normal OB supergiants, and we find that the main difference in mass loss is due to the lower masses of LBVs. In addition, we find that the increase in helium abundance changes the mass-loss properties by small amounts (up to about 0.2 dex in log Mdot), while CNO processing is relatively unimportant for the mass-loss rate. A comparison between our mass loss predictions and the observations is performed for four relatively well-studied LBVs. The comparison shows that (i) the winds of LBVs are driven by radiation pressure on spectral lines, (ii) the variable mass loss behaviour of LBVs during their S Doradus-type variation cycles is explained by changes in the line driving efficiency, notably due to the recombination/ionisation of Fe IV/III and Fe III/II, and finally, (iii) the winds of LBVs can be used to derive their masses, as exemplified by the case of AG Car, for which we derive a present-day mass of 35 Msun.Comment: 12 pages; A&A accepte

On the Mass-Loss Rates of Massive Stars in the Low-Metallicity Galaxies IC 1613, WLM and NGC 3109

We present a spectroscopic analysis of VLT/X-Shooter observations of six O-type stars in the low-metallicity (Z ~ 1/7 Z\odot) galaxies IC 1613, WLM and NGC 3109. The stellar and wind parameters of these sources allow us, for the first time, to probe the mass-loss versus metallicity dependence of stellar winds below that of the Small Magellanic Cloud (at Z ~ 1/5Z\odot) by means of a modified wind momentum versus luminosity diagram. The wind strengths that we obtain for the objects in WLM and NGC 3109 are unexpectedly high and do not agree with theoretical predictions. The objects in IC 1613 tend towards a higher than expected mass-loss rate, but remain consistent with predictions within their error bars. We discuss potential systematic uncertainties in the mass-loss determinations to explain our results. However, if further scrutinization of these findings point towards an intrinsic cause for this unexpected sub-SMC mass-loss behavior, implications would include a higher than anticipated number of Wolf-Rayet stars and Ib/Ic supernovae in low-metallicity environments, but a reduced number of long-duration gamma-ray bursts produced through a single-star evolutionary channel.Comment: 9 pages, 3 figures; accepted for publication in The Astrophysical Journal Letter

Effects Of Thinning On Growth And Sap Flow In Nine-Year-Old Azadirachta Excelsa (Jack) In Merlimau,Melaka, Malaysia

Since 1997, the forest plantation in Malaysia has gained further momentum with the inclusion of selected indigenous species for forest plantation development. Considering the size of plantations being established, the need for studies on silvicultural operation is widely recognized. Until now, except for Acacia mangium, there was no specific model on silviculture and maintenance of each species being planted in Malaysia. The objectives of this study were to quantify the effects of thinning regime on the diameter growth, stand volume and crown structure and to determine the effect of sap flow of thinned and unthinned A. excelsa stands. The study was conducted in the, Sime Darby Estates, Merlimau, Melaka. The A.excelsa stands were planted at an initial spacing of 3 x 4 m (833 stem ha-1) over 2 hectares in May 1995. There were two treatments used for this study; unthinned as control and moderate thinning, where 50% of the stand were felled systematic according to lines. In addition sap flow velocity of selected trees in both treatments were measured using heat pulse probe connected to data logger. During the study, the achieved mean diameter at breast height of A. excelsa was 14.30 ± 0.81 cm and the mean of the potential final crop trees (300 trees ha-1) of 18.99 ± 0.78 cm. The mean periodic annual diameter increment was 1.87 ± 0.07 cm year-1 before thinning and 1.60 ± 0.08 cm year-1 23 months after thinning. The periodical annual diameter increments are not significantly different between plots after 23 months. The diameter increment is still increasing indicating that the growth of the species has not reached the optimum rate. The response to thinning also includes the effect on the expansion of the crowns. Results presented from this trial have indicated that the thinning has a positive effect on crown development in which thinned A.excelsa stand reached up to 6.5 m in length, as compared with the unthined treatment up to 5.0 m. The crown length increment was significantly, being greater by quantify by 30% in the thinned plot. The crown radial of both unthinned and thinned stand varied from 0.2 to 3.6 m and 0.1 to 4.2 m respectively. The amount of water loss in the thinned stand was significantly higher than those in the unthinned plot, 0.53 liter/hour compared with 0.32 liter/hour respectively. The rate of water loss for A. excelsa at thinned stand was higher than those from unthinned stand with a total of 12.02 liters and 10.27 liters over day respectively. Higher soil moisture content was also observed in thinned plot compared to unthinned plot. This study provides useful information on the growth of A.excelsa due to thinning activities by creating the gap opening and the water loss implication after thinning was undertaken. Such information is useful in making long-term growth projections with growth adjusted to variation of microclimate within the stand

Following the Trail of Musical Manuscripts and Prints

Problematika o uporabi, širjenju in dediščini historičnih glasbenih rokopisov in tiskov na širšem evropskem prostoru je prepoznavna tudi skozi delovanje in glasbeno poslanstvo dominikanskega in minoritskega samostana na Ptuju. Obe nekoč izjemno pomembni redovni skupnosti sta bili tesno vpeti v evropska duhovna gibanja. Ohranjena glasbeno-teoretična dela, liturgične knjige in posamezni foliji omogočajo podrobnejše poznavanje glasbene kulture obeh redovnih skupnosti in medkulturnih vplivov, ki so bili posledica pestre migracije redovnikov med samostani obeh redov.The paper focuses on issues concerned with the heritage of historical music manuscripts and prints, along with their use and dissemination in the wider European area, as well as the activities and musical mission of the Dominican and Minorite monasteries in Ptuj (Pettau, Petovio). Both monastic orders were once exceptionally important and maintained strong connections with European spiritual movements. They preserved works on music theory, liturgical books and some sheet music, which has enabled a more detailed insight into the musical culture of monastic communities and into the transcultural influences that resulted from the multi-directional migrations of friars among various European monasteries in the past