O debate sobre os métodos de ensino nos liceus portugueses (anos 30 a 60 do século XX)

Congresso realizado nos dias 6 a 9 de Maio de 2014, em Toluca, MéxicoA presente comunicação tem como objetivo refletir sobre os métodos de ensino, ao nível do ensino secundário, tal como são propostos e debatidos por educadores e professores em duas das grandes revistas pedagógicas consagrados a esse nível de ensino e ligadas a um importante contexto de formação de professores – o Liceu Normal de Pedro Nunes situado em Lisboa. Estamos a falar do Boletim do Liceu Normal de Lisboa Pedro Nunes (1932-1938) e de Palestra. Revista de pedagogia e cultura (1957-1973).info:eu-repo/semantics/publishedVersio

Polarized reflected light from the Spica binary system

Close binary systems often show linear polarization varying over the binary period, usually attributed to light scattered from electrons in circumstellar clouds. One of the brightest close binary systems is Spica (alpha Virginis) consisting of two B-type stars orbiting with a period of just over four days. Past observations of Spica have shown low poClose binary systems often show linear polarization varying over the binary period, usually attributed to light scattered from electrons in circumstellar clouds. One of the brightest close binary systems is Spica (alpha Virginis) consisting of two B-type stars orbiting with a period of just over four days. Past observations of Spica have shown low polarization with no evidence for variability. Here we report new high-precision polarization observations of Spica that show variation with an amplitude of about 200 parts per million. By including polarized radiative transfer in a binary star model, we show that the phase-dependent polarization is mainly due to light reflected from the primary component of the binary system off the secondary component and vice versa. The stars reflect only a few per cent of the incident light, but the reflected light is very highly polarized. The polarization results show that the binary orbit is clockwise and the position angle of the line of nodes is 130.4° ± 6.8°, in agreement with intensity interferometer results. We suggest that reflected light polarization may be much more important in binary systems than has previously been recognized and may be a way of detecting previously unrecognized close binaries.arization with no evidence for variability. Here we report new high-precision polarization observations of Spica that show variation with an amplitude of about 200 parts per million. By including polarized radiative transfer in a binary star model, we show that the phase-dependent polarization is mainly due to light reflected from the primary component of the binary system off the secondary component and vice versa. The stars reflect only a few per cent of the incident light, but the reflected light is very highly polarized. The polarization results show that the binary orbit is clockwise and the position angle of the line of nodes is 130.4° ± 6.8°, in agreement with intensity interferometer results. We suggest that reflected light polarization may be much more important in binary systems than has previously been recognized and may be a way of detecting previously unrecognized close binaries

HIPPI-2 : a versatile high-precision polarimeter

We describe the High-Precision Polarimetric Instrument-2 (HIPPI-2) a highly versatile stellar polarimeter developed at the University of New South Wales. Two copies of HIPPI-2 have been built and used on the 60-cm telescope at Western Sydney University's (WSU) Penrith Observatory, the 8.1-m Gemini North Telescope at Mauna Kea and extensively on the 3.9-m Anglo-Australian Telescope (AAT). The precision of polarimetry, measured from repeat observations of bright stars in the SDSS g′band, is better than 3.5 ppm (parts per million) on the 3.9-m AAT and better than 11 ppm on the 60-cm WSU telescope. The precision is better at redder wavelengths and poorer in the blue. On the Gemini North 8-m telescope, the performance is limited by a very large and strongly wavelength-dependent TP that reached 1000's of ppm at blue wavelengths and is much larger than we have seen on any other telescope

Photometric update of δ Scuti stars : ZZ Microscopium

Multi-color CCD photometric update of the bright high amplitude δ Scuti star ZZ Microscopium (ZZ Mic) is presented. We find that the B band has the highest amplitude at 0.47 mag while the V band amplitude is smaller at 0.38 mag. The revised pulsation period 0.06717850 day is similar to most recent previous estimates. We did not detect secondary mode pulsations. We find the temperature of the star varies by 720 K during pulsations and its radius changes by 0.1 R☉. We estimate the mass of ZZ Mic as 1.93 M☉ and surface gravity g as 4.19

Analysis of dual band and survey photometry of two low mass ratio contact binary systems

The study presents photometric analysis of the completely eclipsing contact binary systems TYC 8351-1081-1 and ASAS J210406-0522.3. TYC 8351-1081-1 is an extremely low mass ratio (q= 0.086) system with a high degree of contact (f= 0.66) while ASAS J210406-0522.3 is found to be in marginal contact (f= 0.08) with a relatively low-mass ratio of 0.272. There is good thermal contact in both systems with only a small difference in the temperature of the components. The systems have been observed by a number sky surveys over the past 20 years. We compare the light curve solutions from up to three of these surveys and find that survey photometric data manually analysed is robust and yields results comparable to dedicated ground-based photometry. There is evidence of significant luminosity transfer from the primary to the secondary, on the order of 0.5L⊙ for TYC 8351-1081-1 and 0.06L⊙ for ASAS J210406-0522.3. There appears to be no change in the period of either system over the past 20 years and theoretical angular momentum loss is below current measurement threshold in both cases. We also show that the mass ratio and separation are well above the theoretical values for orbital instability in both cases. As would be expected, the density of the secondary components is significantly higher relative to the primary

PICSARR : high-precision polarimetry using CMOS image sensors

We have built and tested a compact, low-cost, but very high performance astronomical polarimeter based on a continuously rotating half-wave plate and a high-speed imaging detector. The polarimeter is suitable for small telescopes up to ∼1 m in aperture. The optical system provides very high transmission over a wide wavelength range from the atmospheric ultraviolet cut-off to ∼1000 nm. The high quantum efficiency, low noise, and high speed of the detectors enable bright stars to be observed with high precision as well as polarization imaging of extended sources. We have measured the performance of the instrument on 20 and 60 cm aperture telescopes. We show some examples of the type of science possible with this instrument. The polarimeter is particularly suited to studies of the wavelength dependence and time variability of the polarization of stars and planets

Multi-band aperture polarimetry of Betelgeuse during the 2019-20 dimming

Betelegeuse (α Orion) is a red supergiant (M2 Iab) and a semi-regular long period variable (SRc) with periods prominent around 400 and 2100 days (Montarg`es et al. 2016). Its most recent dimming event was first noticed by Guinan et al. (2019), who subsequently determined the minimum magnitude to be the lowest on record (Guinan et al. 2020), and whose reporting catalysed other observations. New VLT-SPHERE images, when compared to those from a year earlier, reveal a darkened lower hemisphere (Montarg`es et al. 2020). Levesque & Massey (2020) analysed their own spectrophotometry in the context of those images, finding the photosphere temperature to be nearly unchanged and attributing Betelgeuse’s dimming to episodic mass-loss and a subsequent increase in large grain circumstellar dust. Aperture polarimetry was used extensively in the study of late-type supergiant variability until the 1980s (Clarke 2010). Betelgeuse, like similar stars, can be highly polarised at blue wavelengths reducing ∝ λ −4 to a minimum at red and reversing in the infrared; it undergoes slow changes in both polarisation magnitude (p) and position angle (ζ), on similar timescales to, but not necessarily correlated with its photometric periods. The most popular explanations relate to absorption and scattering from either convective cells (hotspots), circumstellar dust or both. Auri`ere et al. (2016) describe a scenario where near-surface features induce a net polarisation by asymmetrically depolarising the continuum. The polarisation behaviour then depends on feature geometry and composition. Recent polarimetric imaging with SPHERE-ZIMPOL provides justification for both mechanisms (Kervella et al. 2016); such measurements provide superior detail, but the resources required restrict their frequency. (Please note an erratum for this article is available via https://iopscience.iop.org/article/10.3847/2515-5172/ab83fc/meta.

Photometric analysis of two extreme low mass ratio contact binary systems

Multi-band photometry and light curve analysis for two newly recognized contact binary systems, TYC 6995–813–1 and NSVS 13602901, are presented. Both were found to be of extreme low mass ratios 0.11 and 0.17, respectively. The secondary components of both systems show evidence of considerable evolution with elevated densities as well as both luminosity and radii well above their main sequence counterparts. Even in the absence of significant spot activity, at least one of the systems, TYC 6995–813–1, displays features of magnetic and chromospheric activity. TYC 6995–813–1 is also determined to be a potential merger candidate with its current separation near the theoretical instability separation

On the true nature of the contact binary CRTS J192848.7-404555

CRTS J192848.7-404555 was recognized as a potential contact binary merger candidate on the basis of survey photometry analysis. We have carried out follow-up ground-based photometry of the system and showed that at the recorded coordinates for the system, there are two stars approximately 3 s of arc apart. Our analysis shows that the fainter of the two stars is the actual variable while the slightly brighter star is of fixed brightness. In addition, we show that the reported survey photometry is the result of both stars being treated as a single light source with resultant erroneous light curve solution. The true nature of CRTS J192848.7-404555 shows it to be a low mass contact binary system with a high mass ratio of 0.425, high amplitude of 0.69 magnitude, and shallow 24% contact. The system does not have features of orbital instability and is not a potential merger progenitor

Radio-continuum study of the supernova remnants in the large magellanic cloud - an SNR with a highly polarised breakout region - SNR J0455-6838

We present the results of new moderate resolution ATCA observations of SNR J0455-6838. We found that this SNR exhibits a mostly typical appearance with rather steep and curved α=-0.81±0.18 and D=43x31±1 pc. Regions of high polarisation were detected, including unusually strong (~70%) region corresponding to the northern breakout. Such a strong polarisation in breakout regions has not been observed in any other SNR