Monthly Archives: November 2012

Timelapse of the Total Solar Eclipse

Last week I shared some of the images I obtained during the Total Solar Eclipse on 13 / 14 November 2012. It was observed from the Mulligan Highway, 44 km south of Lakeland, Queensland Australia. After spending a weekend playing with the raw frames, I ended up with this timelapse video, which shows all the sequence of the eclipse.

Timelapse video of the Total Solar Eclipse on 13 / 14 Nov 2012. The direct link to YouTube is here. Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University, Agrupación Astronómica de Córdoba / Red Andaluza de Astronomía).

The video combines 1203 individual frames obtained while the eclipse was happening. As before, I used my refractor Skywatcher telescope, 80 mm aperture and 600 mm focal, and my digital camera CANON EOS 600D at primary focus. For all partial phases but the totality I used a solar filter which blocks the 99.9997% of the incident light. The approximate field of view of the video is 2ºx1º. I usually took a frame each 6 seconds, but sometimes I triggered many consecutive images to improve the quality of the final photo of that moment. The music is the theme “WorldBuilder” written by Fran Solo and included in Epic Soul Factory Xpansion Edition.

Total Solar Eclipse 13 / 14 Nov 2012

After many years waiting for it, I have finally observed (and enjoyed!) my very first Total Solar Eclipse. It was on 14 November 2012 (still 13 November following time in UT) and I was 45 km south of Lakeland, Queensland Australia (I had to drive during the night trying to escape from the clouds in the coast near Port Douglas). Here you have some of the images I have obtained of this rare phenomenon.

My sequence of the Total Solar Eclipse on 13 / 14 November 2012, 50 km south from Lakeland, Queensland, Australia. I used a Skywatcher D 80mm, F 600mm, primary focus using CANON EOS 600D. All times given in UT and correspond to 13 Nov 2012. Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University, Agrupación Astronómica de Córdoba / Red Andaluza de Astronomía).

Some more pictures:

The sun rises, but the eclipse did already start. Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University, Agrupación Astronómica de Córdoba / Red Andaluza de Astronomía).

Image of the totality showing the brightest areas of the solar corona and some solar prominences close to the lunar limb (in red). Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University, Agrupación Astronómica de Córdoba / Red Andaluza de Astronomía).

Image of the totality showing the diffuse solar corona, but the brightest areas are overexposed. Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University, Agrupación Astronómica de Córdoba / Red Andaluza de Astronomía).

Diamond ring, the first light of the Sun coming after the totality. Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University, Agrupación Astronómica de Córdoba / Red Andaluza de Astronomía).

HDR (High Dynamic Range) image combining 20 individual frames with different exposition times. Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University, Agrupación Astronómica de Córdoba / Red Andaluza de Astronomía).

The importance of massive stars

The mass range of stars drawing their energy supply from nuclear fusion covers about three orders of magnitude. The least massive stars known have masses around 0.1 solar masses (M) and the most massive examples are around 100 M, although stars with masses of ~150M may also exist.

Massive stars are defined as those stars with masses higher than around 8 M. However, this lower limit is not completely fixed, as the definition of massive star actually comes from those stars that ignite helium and afterwards carbon in non-degenerated stellar cores (i.e., the hydrostatic equilibrium is reached because the inward gravitational force is balanced with the outward force due to the pressure gradient of the gas). Depending on the evolutionary scenario, this happens between 7 and 9 M.

Massive stars consume their fuel faster than low and intermediate mass stars: a solar-mass star has a life ~125 times longer than a 10 M star. Massive stars also are very luminous: a 100M star shines with a luminosity similar to ~1600 Suns. Hence, except for stars of transient brightness, like novae and supernovae, hot, massive stars are the most luminous stellar objects in the Universe.

Young, massive star clusters near the center of the Milky Way, at ~25,000 light-years from Earth: the Arches cluster (left) and the Quintuplet Cluster (right). Both pictures were taken using infrared filters by the NICMOS camera of the Hubble Space Telescope in September 1997. The galactic center stars are white, the red stars are enshrouded in dust or behind dust, and the blue stars are foreground stars between us and the Milky Way’s center. The clusters are hidden from direct view behind black dust clouds in the constellation Sagittarius. Credit: Don Figer (STScI) and NASA.

Massive stars are, however, extremely rare. Following the very famous results obtained by the Austrian-Australian-American astrophysicist Edwin Ernest Salpeter in 1955, the number of stars formed per unit mass interval is roughly proportional to M -2.35. Therefore we expect to find only very few massive stars in comparison with solar-type stars: for each 20M star in the Milky Way there are roughly a hundred thousand solar-type stars; for each 100M star there should be over a million solar-type stars.

However, despite their relative low number, massive stars have a fundamental influence over the interstellar medium and galactic evolution because they are the responsible of the ionization of the surrounding gas and they deposit mechanical energy first via strong stellar winds and later as supernovae, enriching the interstellar medium by returning unprocessed and nuclear processed material during their whole life. Massive stars therefore condition their environment and supply it with new material available for the birth of new generations of stars, being even the triggering mechanism of star formation. They also generate most of the ultraviolet ionization radiation in galaxies, and power the far-infrared luminosities through the heating of dust. The combined action of stellar winds and supernovae explosions in massive young stellar clusters leads to the formation of super-bubbles that may derive in galactic super-winds. Furthermore, massive stars are the progenitors of the most energetic phenomenon nowadays found, the gamma-ray bursts (GRBs), as they collapse as supernova explotions into black holes. Particularly, the interest in hot luminous stars has increased in the last decade because of the massive star formation at high redshift and the results of numerical simulations regarding the formation of the fi rsts stars at zero metallicity (Population III stars), that are thought to be very massive stars with masses around 100 100M.

The descents of the most massive, extremely hot (temperatures up to 200,000 K) and very luminous (105  to 106 solar luminosities, L) O stars are Wolf-Rayet stars, which have typical masses of 25 – 30 M for solar metallicity.

The Crescent Nebula

A very nice example of a nebula surrounding a Wolf-Rayet star is the so-called Crescent Nebula (NGC 6888, Caldwell 27, Sharpless 105). Located in the northern constellation of Gygnus, The Swan, it lies at around 5000 light years from us. The Crescent Nebula has been formed by the strong stellar winds of the Wolf-Rayet star WR 136 (HD 192163), which is located in the center of the nebula. This is an image of the Crescent Nebula I took in 2004 using the 2.5m Isaac Newton Telescope (INT) at the Roque de los Muchachos Observatory (La Palma, Spain) while I was still preparing my PhD Thesis at the Instituto de Astrofísica de Canarias (IAC, Tenerife, Spain) about the properties of dwarf galaxies hosting Wolf-Rayet stars. Actually, the image was taken during the twilight, when sky is still dark enough the get details in the narrow-band filters.

Crescent Nebula using narrow-band filters, by Angel R. Lopez-Sanchez

Image of the Crescent Nebula (NGC 6888) obtained by the author combining data using the broad-band optical B filter (blue) and the narrow-band optical filters [O III] (green) and Hα (red) obtained using the Wide Field Camera (WFC) attached at the 2.5m Isaac Newton Telescope (INT) at the Roque de los Muchachos Observatory (La Palma, Spain). The size of the image is around 22 x 22 arcminutes, just slightly smaller than the field of view of the full moon in the sky (30 arcminutes in diameter). Credit: Ángel R. López-Sánchez

The complex structure of the Crescent Nebula is a consequence of the interaction of the strong wind of the Wolf-Rayet star with material ejected by the star in an earlier phase, probably while it was a red supergiant. The actual loss-mass rate of the WR136 is around 0.00001 solar masses per year, which means the star losses the equivalent of the Sun’s mass every 10,000 years.

The image clearly shows ionized gas (nebular emission) with very different conditions: while red-color (Hα emission) is tracing the normal, emitting ionized gas, the green colour ([O III] emission) indicates regions with high excitation of the gas, meaning higher temperatures probably because of shocks. In just some few hundreds of years the star will explode as type-II supernova and destroy all the nebula, although it will create a new object: a supernova remnant.