The star formation history of RCW 36

Recent studies of massive-star forming regions indicate that they can contain multiple generations of young stars. These observations suggest that star formation in these regions is sequential and/or triggered by a previous generation of (massive) stars. Here we present new observations of the star forming region RCW 36 in the Vela Molecular Ridge, hosting a young cluster of massive stars embedded in a molecular cloud complex. In the periphery of the cluster several young stellar objects (YSOs) are detected which produce bipolar jets (HH 1042 and HH 1043) demonstrating that these objects are still actively accreting. The VLT/X-shooter spectrum of the jet structure of HH 1042 provides detailed information on the physical conditions and kinematical properties of the jet plasma. From this information the YSO's accretion history can be derived. Combining the photometric and spectroscopic observations of RCW 36 gives insight into the formation process of individual stars and the star formation history of this young massive-star forming region.Comment: 10 pages, 5 figures, to appear in the proceedings of the ESO workshop "Circumstellar Dynamics at High Resolution", Foz do Iguacu (Br), Feb 2012, eds. A. Carciofi and T. Riviniu

Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)

Among the competing evolution theories for subdwarf-B (sdB) stars is the binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary system consisting of a pulsating sdB star and a late F main-sequence companion (O'Donoghue et al. 1997), however the period and the orbit semi-major axes have not been precisely determined. This paper presents orbital characteristics of the EC 20117-4014 binary system using 20 years of photometric data. Periodic Observed minus Calculated (O-C) variations were detected in the two highest amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating the binary system's precise orbital period (P = 792.3 days) and the light-travel time amplitude (A = 468.9 s). This binary shows no significant orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3 $\sigma$ as an upper limit). This upper limit of the eccentricity is the lowest among all wide sdB binaries with known orbital parameters. This analysis indicated that the sdB is likely to have lost its hydrogen envelope through stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB stars. In addition to those results, the underlying pulsation period change obtained from the photometric data was $\dot{P}$ = 5.4 ($\pm$0.7) $\times$ $10^{-14}$ d d$^{-1}$, which shows that the sdB is just before the end of the core helium-burning phase

On the Reliability of Cross Correlation Function Lag Determinations in Active Galactic Nuclei

Many AGN exhibit a highly variable luminosity. Some AGN also show a pronounced time delay between variations seen in their optical continuum and in their emission lines. In effect, the emission lines are light echoes of the continuum. This light travel-time delay provides a characteristic radius of the region producing the emission lines. The cross correlation function (CCF) is the standard tool used to measure the time lag between the continuum and line variations. For the few well-sampled AGN, the lag ranges from 1-100 days, depending upon which line is used and the luminosity of the AGN. In the best sampled AGN, NGC 5548, the H_beta lag shows year-to-year changes, ranging from about 8.7 days to about 22.9 days over a span of 8 years. In this paper it is demonstrated that, in the context of AGN variability studies, the lag estimate using the CCF is biased too low and subject to a large variance. Thus the year-to-year changes of the measured lag in NGC 5548 do not necessarily imply changes in the AGN structure. The bias and large variance are consequences of finite duration sampling and the dominance of long timescale trends in the light curves, not due to noise or irregular sampling. Lag estimates can be substantially improved by removing low frequency power from the light curves prior to computing the CCF.Comment: To appear in the PASP, vol 111, 1999 Nov; 37 pages; 10 figure

Pengaruh Pemberian Vitamin a, B12, C Dan Kombinasi Ketiganya Melalui Drinking Water Terhadap Panjang Dan Bobot Tulang Femur, Tibia Dan Tarsometatarsus Puyuh (Coturnix Coturnix Japonica L.)

Produktivitas puyuh (Coturnix coturnix japonica L.) yang meningkat merupakan pencapaian utama dari kegiatan beternak. Hal tersebut didukung oleh proses metabolisme yang baik, sehingga untuk menjaga proses tersebut agar berjalan dengan baik maka dibutuhkan vitamin pada ransum. Vitamin adalah zat yang dibutuhkan dalam jumlah sedikit oleh tubuh yang berpengaruh terhadap kesehatan tubuh serta dalam proses pertumbuhan, perkembangan dan reproduksi. Penelitian ini bertujuan untuk mendapatkan alternatif optimalisasi perkembangan dengan manajemen pemberian suplemen pada puyuh yaitu vitamin A, B12, C dan kombinasi ketiganya melalui drinking water. Perlakuan dimulai pada saat puyuh berumur 29 hari sampai umur 63 hari. Paramater dalam penelitian ini adalah panjang dan bobot tulang femur, tibia dan tarsometatarsus. Penelitian ini menggunakan Rancangan Acak Lengkap (RAL), seluruh data dianalisis dengan Analysis of Varian (ANOVA). Hasil analisis yang berbeda nyata diuji dengan uji lanjut Jarak Berganda Duncan pada taraf kepercayaan 95%. Hasil penelitian menunjukkan bahwa pemberian larutan vitamin A, B12, C dan kombinasi ketiganya memberikan perbedaan tidak nyata terhadap panjang dan bobot tulang femur, tibia dan tarsometatarsus. Berdasarkan hasil penelitian ini dapat disimpulkan bahwa pemberian larutan vitamin tersebut tidak berpotensi untuk memacu pertumbuhan dan perkembangan tulang puyuh

Applicability and fairness of the oral examination in undergraduate psychiatry training in South Africa

Objective: There are several methods of evaluating medical students’ performance, such as written examination, oral examination and objective structured clinical examination (OSCE). Many studies have focused on the reliability and validity of these methods but few studies have explored comparison between these methods. Psychiatry is the only subject at the University of Stellenbosch where the final assessment consists of solely an oral component. The aim of the study was to compare students’ final overall and discipline specific examination marks (i.e. in the other subjects) with the examination marks in psychiatry, and to determine if content or structure (e,g. oral, written or OSCE format) of examination impacts more on the student performance in the examination. Method: 343 final year medical students were included. All undertook their psychiatry rotation at the University of Stellenbosch, South Africa during 2008 and 2009. Data of marks obtained in all the disciplines during 2008 and 2009 were collected and class marks were compared with their final examination marks across all disciplines. Bland-Altman plots were used to assess the level of agreement between the class and examination marks. Cases below the lower threshold were compared to all other cases across all disciplines. The odds ratio for group status was calculated for gender distribution of examiners. Results: The psychiatry class mark and final oral examination mark provided similar measures within a width of 31.5. Cases below the threshold had poorer performance in two other disciplines. The gender distribution of the examiners (female-female) significantly increased the odds ratio for poorer performance in the oral examination.Conclusion: The results suggest that a group of students underperform in their final examination independent of method of evaluation and that the gender of examiners impacts on examination marks. Therefore future research should focus on identifying and modifying factors (including choice of examiner combinations) that contribute to the poor performance of medical students in their final examination, in order to help students perform better. Gender distribution of examiners should also be considered when examinations are structured and designed.Keywords: Oral; Medical; Student; Gender; Examiner; Performance; OSC

A photometric monitoring of bright high-amplitude delta Scuti stars. II. Period updates for seven stars

We present new photometric data for seven high-amplitude delta Scuti stars. The observations were acquired between 1996 and 2002, mostly in the Johnson photometric system. For one star (GW UMa), our observations are the first since the discovery of its pulsational nature from the Hipparcos data.The primary goal of this project was to update our knowledge on the period variations of the target stars. For this, we have collected all available photometric observations from the literature and constructed decades-long O-C diagrams of the stars. This traditional method is useful because of the single-periodic nature of the light variations. Text-book examples of slow period evolution (XX Cyg, DY Her, DY Peg) and cyclic period changes due to light-time effect (LITE) in a binary system (SZ Lyn) are updated with the new observations. For YZ Boo, we find a period decrease instead of increase. The previously suggested LITE-solution of BE Lyn (Kiss & Szatmary 1995) is not supported with the new O-C diagram. Instead of that, we suspect the presence of transient light curve shape variations mimicking small period changes.Comment: 11 pages, 15 figures, accepted for publication in A&

A survey for pulsating subdwarf B stars with the Nordic Optical Telescope

A search programme for pulsating subdwarf B stars was conducted with the Nordic Optical Telescope on La Palma over 59 nights between 1999 and 2009. The purpose of the programme was to significantly extend the number of rapidly pulsating sdB stars to better understand the properties of this new group of variable compact stars. Candidates were selected initially from the HS and HE surveys, but were supplemented with additional objects from other surveys. Short sequences of time-series photometry were made on the candidates to determine the presence of rapid pulsations. In total twenty new pulsators were found in this survey, most of which have already been published and some extensively studied. We present four new short period pulsators, bringing the total of such pulsators up to 49. We also give limits on pulsation amplitudes for 285 objects with no obvious periodic variations, summarise the results of the survey, and provide improved physical parameters on the composite pulsators for which only preliminary estimates were published earlier.Comment: 17 pages, accepted for publication in A&

Observations of the pulsating subdwarf B star Feige 48: Constraints on evolution and companions

Since pulsating subdwarf B (sdBV or EC14026) stars were first discovered (Kilkenny et al, 1997), observational efforts have tried to realize their potential for constraining the interior physics of extreme horizontal branch (EHB) stars. Difficulties encountered along the way include uncertain mode identifications and a lack of stable pulsation mode properties. Here we report on Feige 48, an sdBV star for which follow-up observations have been obtained spanning more than four years, which shows some stable pulsation modes. We resolve the temporal spectrum into five stable pulsation periods in the range 340 to 380 seconds with amplitudes less than 1%, and two additional periods that appear in one dataset each. The three largest amplitude periodicities are nearly equally spaced, and we explore the consequences of identifying them as a rotationally split l=1 triplet by consulting with a representative stellar model. The general stability of the pulsation amplitudes and phases allows us to use the pulsation phases to constrain the timescale of evolution for this sdBV star. Additionally, we are able to place interesting limits on any stellar or planetary companion to Feige 48.Comment: accepted for publication in MNRA