ING Scientific Highlights in 1993
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ING Scientific Highlights
in 1993*

*Astronomical discoveries following from observations carried out with the ING telescopes


[ 1992 Scientific Highlights | 1994 Scientific Highlights ]


Supernova 1993JOn March 28th 1993, supernova 1993J was discovered in M81. After SN1987A, this was the closest core-collapse supernova to have occurred this century and the closest observable from the north. RGO and La Palma astronomers immediately set in motion an extensive programme of astrometric, photometric (UVBRI) and low- and high- dispersion spectroscopic monitoring. The INT spectrum of SN1993J obtained one day after the discovery was the first recorded anywhere at any wavelength. Early spectra yielded a reliable estimate of the extinction towards the supernova, enabling a bolometric light curve to be calculated. Shortly after being collected, data are copied to RGO in Cambridge where they are reduced on a timescale of a few days. They are then placed in an on-line archive which can be accessed from anywhere in the world. In this manner the most comprehensive set of optical photometric and spectroscopic data is being offered to the community. Over 70 sites worldwide have availed themselves of this unique facility.

The initial optical rise of the supernova was very rapid, reaching maximum only about 3 days after the explosion date. The presence of hydrogen lines in the spectrum showed that SN1993J was a type II event. Unusually, the UBVRI light curves went through two maxima at 3 and 20 days after the explosion. To study the evolution of the supernova luminosity a bolometric (UV, optical and IR) light curve was derived using La Palma UBVRI photometry plus infrared observations from other observatories. It was shown that the supernova peak luminosity exceeded 2.5 x 109 solar luminosities and the temperature peaked at over 17000K. The supernova cooled rapidly to 8000K, with the photospheric velocity declining from 13000 to 4000 kms-1. The second rise was brought about by the decay energy released from 56Ni created deep in the core of the explosion. The decay energy diffused (and mixed) upwards, eventually meeting the recombination wave which was moving inwards with respect to the ejecta.

The rapid initial decline of the light curve and the speed with which it went into the second rise implies that at the time of the explosion, the progenitor must have been a relatively low mass for a type II explosion. The hydrogen envelope was probably less than 0.5 solar masses and the helium mantle could not have been larger than about 4 solar masses. This, in turn, implies the progenitor mass was about 15 solar masses on the main sequence, including about 10 solar masses of hydrogen. Thus, as the progenitor evolved, it must have lost about 10 solar masses of its envelope. The most likely mechanism for this mass loss is via mass transfer to a close companion. Indeed the transfer may have become so rapid that a common envelope, extending as far as one light year, might have been generated. Thus the picture of the supernova progenitor which has developed is a K supergiant which, by the time it exploded, had been stripped of most of its hydrogen envelope due to mass loss onto a companion blue supergiant.

Among the evidence that SN1993J does indeed have an extended envelope released before the explosion is the observation of very narrow optical emission lines in the early spectra. These lines are caused by ionisation of a progenitor wind by the extreme ultraviolet flash from the supernova, followed by its recombination. In addition, near infrared photometry, when compared with ING optical photometry, reveals the development of an infrared excess since about day 50. The most plausible explanation is an infrared echo, ie the re-radiation of the supernova light released near maximum by dust in the progenitor wind lying some light months from the supernova

By day 50, the bolometric light curve was falling exponentially with a e-folding time of 54 days. There was no observed slowdown for a long period. This is quite different from the behaviour of SN1987A where there was a period of 100 days in which the bolometric light curve slowed to match the radioactive decay (with an e-folding time of 111 days). This also points to a low mass in SN1993J: as early as day 50 a significant and increasing fraction of the gamma rays from the 56Ni must have been escaping.

About a month after the explosion, the SN1993J spectrum appeared less and less like that of a type II event. Helium, oxygen and calcium lines increased in prominence, suggesting that the supernova was changing into a type Ib event. Supernova of type Ib form a rather mysterious subclass thought to arise from massive progenitors which have lost their hydrogen envelopes. More ING spectra, obtained when the supernova was about 300 days old, confirm its metamorphosis into a type Ib. SN1993J may be a kind of missing link between type II and type Ib. It suggests that rather than there being discrete sub-types of core collapse supernovae, there is in fact a continuum of progenitors with a range of hydrogen envelope masses.

During the first few nights following the discovery of supernova 1993J, researchers observed the interstellar Ca II and Na I absorption lines in its spectrum at high spatial resolution (FWHM ~ 5-6 kms-1) using the Utrecht Echelle Spectrograph on the WHT. They found a crowd of absorption components in the radial velocity range between -135 and +165 kms-1. In order to understand the features, the group re-examined previous surveys of local interstellar gas, high velocity gas and intergalactic gas in the field. They also observed the line of sight to the supernova at 21cm using the 100m radio telescope at Effelsberg. The components between -85 and -165 kms-1 originate in intergalactic gas within the M81 group of galaxies which has been tidally pulled from one of the galaxies in the group. Components at -135 and -119 kms-1 originate within M81, indicating that the supernova is embedded in the inner region of the galaxy. The remaining components arise in our own galaxy, including the halo.

More information

ING facilities involved: 

  • Isaac Newton Telescope, using prime focus CCD camera and IDS
  • William Herschel Telescope, using ISIS and FOS2
  • Jacobus Kapteyn Telescope, using CCD camera
Some references: 
  • Lewis, J.R. et al, 1994, "Optical observations of supernova 1993J from La Palma - Part One - Days 2 to 125", MNRAS, 266, L27 
  • Meikle, P. et al, 1993, "Supernova 1993J", GEMINI Royal Greenwich Obs. Newsletter, 40, 1 
  • Vladilo, G. et al, 1993, "Interstellar and intergalactic gas in the direction of supernova 1993J", A&A, 280, L11 



In 1950 Jan Oort inferred the existence of a huge comet cloud surrounding the solar system. Today the 'Oort Cloud' is an accepted part of the Solar System, containing perhaps 1012 comets up to 50000 astronomical units (au) from the Sun, though none have actually been detected. Gerard Kuiper hypothesised that there might be a second comet cloud much nearer than the Oort Cloud. At distances greater than 40 - 50 au the space density of proto-planetary material would be too low to support continued accretion of bodies to sizes greater than a few hundred kilometres across, but it seemed unlikely that accumulation would stop sharply at 30 - 40 au (the Neptune-Pluto distance). Naturally these comets would be extremely faint due to their large distance and assumed low visual albedo. Several searches took place between 1989 and 1992 using both photographic and CCD techniques, but all were unsuccessful until the first such object, 1992 QB1, was finally discovered by researchers using deep CCD images. They discovered a second, 1993FW, six months later. The INT prime focus camera with the large format Ford-Loral CCD is ideal for the search for trans-Neptunian objects since the pixel size of 0.37 arcseconds allows adequate sampling even during sub-arcsecond seeing, while the large area of 12.6 arcminutes square enhances the probability of detection. 

In September 1993 researchers obtained 30 minute R band images in clear weather and good seeing, achieving a limiting magnitude of R=23. Objects at distances of more than 30 au slowly retrograde along the ecliptic at velocities of less than 4 arcseconds per hour, and so images of fields were obtained at least 2 hours apart, and were compared to reveal any moving objects. The search revealed two trans-Neptunian objects, named 1993 SB and 1993 SC. 1993 SB was barely visible at R=22.7, while 1993 SC was much easier to detect at R=21.7. Analysis of the positions by Marsden of the International Astronomical Union gave initial circular orbits of radii 33.1 au and 34.5 au respectively. Both are located approximately 60 degrees away from Neptune in heliocentric longitude, and therefore there is a small possibility that they could be Neptune Trojans librating around the L4 Lagrangian point in the Sun-Neptune system.

More information

ING facilities involved: 

  • Isaac Newton Telescope, with prime focus CCD
Some references: 
  • Williams, I. et al, 1993, "1993 SB and 1993 SC", IAU Circular, 5869 
  • Williams, I. et al, 1995, "The slow moving objects 1993 SB and 1993 SC", Icarus, 116, 180 


Researchers have been carrying out a major analysis of over 40000 observations of Saturn's satellites spanning the period 1874 to 1989. Both visual (between 1874 and 1947) and photographic (between 1966 and 1989) observations have been analysed. In collaboration with other researchers they have obtained further observations of the satellites of the outer planets using the CCD camera on the JKT. The 1991 Saturn satellite data have been reduced, giving a satellite-satellite rms deviation of 0.10 arcseconds (650km at the distance of Saturn), comparable with the best photographic results. Not only are CCD observations able to produce satellite positions as good as photographic methds, but they are easier to make and reduce. New improved parameters describing the motion of seven of the satellites have been deduced, leading in turn to improved determinations of the masses of the satellites. This work will be of considerable value as part of the planning for the NASA/ESA Cassini/Huygens mission which will place a spacecraft in orbit around Saturn in the early part of next century.

More information

ING facilities involved: 

  • Jakobus Kapteyn Telescope, with CCD camera
Some references: 
  • Beurle, K. et al, 1993, "Preliminary analysis of CCD observations of Saturn's satellites", A&A, 269, 564 
  • Harper, D. et al, 1997, "CCD Astrometry of Saturn's satellites 1990-1994", A&AS, 121, 65 



Observed low-resolution spectrum of Barnard 29, with theoretical spectra superimposedMost stars pass through a brief evolutionary phase towards the end of their lifetimes known as the post-asymptotic giant branch or post-AGB. Lasting 10000 years or less, this is one of the shortest and least-well understood stages of stellar evolution. However, many of these stars reveal anomalous chemical compositions that cannot be understood in terms of the nucleosynthesis and dredge-up processes that occur on the AGB. Researchers used the UES on the WHT to obtain complete spectral coverage in the wavelength range 3850-4950Å of the hot post-AGB star Barnard 29 in the globular cluster M13. A typical metallicity of -1.64 ± 0.11 dex was derived, in agreement with the mean [Fe/H] value from previous M13 studies. More importantly, carbon is depleted by more than 2.0 dex, and nitrogen is enhanced. This result establishes the existence of a class of carbon-poor post-AGB objects which have undergone the first and second dredge-ups but have left the AGB before the onset of the third dredge-up in which carbon is brought to the stellar surface. 

Observed spectrum of HD 56126Other researchers observed the post-AGB star HD56126 also with the UES on the WHT using two different grating settings covering the wavelength range 4380-10410Å. The spectrum is rich in absorption lines from s-process elements such as zirconium, ytrium and lanthanum which are brought to the stellar surface by dredge-up. This confirms the post-AGB nature of the star. But the most important and unexpected result was the detection of diatomic carbon C2 and CN absorption lines in the optical spectrum. A study of these lines shows that they are formed in the AGB remnant. This is the first time that molecular lines from an AGB remnant have been detected in absorption at optical wavelengths. A comparison of the expansion velocity of optical molecular lines with the submillimetre data allows a new field of study of the asymmetry of the AGB remnant. The UES is ideal for this kind of study because of its large wavelength coverage. 

More information

ING facilities involved: 

  • William Herschel Telescope, using UES
Some references: 
  • Conlon, E. et al, 1994, "Abundance analysis of the hot post-AGB star Barnard 29", A&A, 290, 897 
  • Bakker, E. et al, 1996, "Detection of C2, CN and NaI D absorption in the AGB remnant of HD 56126", A&A, 310, 893 



Image of ring in NGC 4736Two TAURUS H alpha data cubes were taken in May 1987 of the inner ring of bright HII regions in the nearby galaxy NGC4736 (M94) have been reduced, combined and analysed. This ring is of particular interest for the dynamics of galaxies, as it shows mild yet significant deviations from circular rotation, indicating either bulk streaming motions or a tilt with respect to the 'normal disk' of the galaxy. 

The spatial resolution of the data, sampled in fully three dimensions, is unprecedented. It allows detailed analysis of the gas morphology and kinematics. The inclination and major axis position angle were derived from the morphology of the H II distribution and from the kinematics, which also allowed the determination of the kiematic centre position, the systematic velocity, and the rotation velocity of the gas in the ring as a function of radius. Subtraction of a model velocity field, constructed using parameter values found from the kinematics, confirms the presence of velocities deviating significantly from circular rotation in the south-eastern quadrant of the ring, as found by earlier workers.

More information

ING facilities involved: 

  • William Herschel Telescope, using TAURUS
Some references: 
  • Mulder, P.S., 1995, "Optical morphology and kinematics of the inner regions of NGC 4736", A&A, 303, 57 



U-band image of quasar
field taken with the WHTWhen absorbing material with a sufficiently high hydrogen column density is located in front of a distant QSO (as viewed from the Earth), a very pronounced discontinuity is produced in the spectrum of the QSO near 912Å, the Lyman limit, in the rest frame of the absorber. the identification of galaxies responsible for such absorption systems leads to a wealth of information about the distribution and evolution of galaxies at high redshift. Researchers have used the WHT to extend this work to galaxies producing Lyman limit systems at z=3. Such galaxies are expected to have a nearly flat continua longwards of the Lyman break, and to be undetectable shortwards of the break because of intrinsic and intervening absorption by neutral hydrogen. They can thus be recognised in deep images taken through appropriately chosen filters, one of which includes the region below the Lyman limit. At z=3 this region is redshifted into the observable U band and ultra deep imaging in U is therefore the key to successful identification. The Tektronix chip at the auxiliary port of the WHT is ideal for this work because of the combination of good seeing, fine spatial sampling and high sensitivity. This programme has been highly successful. In all four fields imaged so far there is an object close to the sight line with the colours expected for a galaxy at the redshift of the QSO absorber. Such objects are therefore the most likely candidates identified so far for 'normal' galaxies at z=3; they have luminosities typical of a large spiral. The projected separations from the QSO sight line and therefore their approximate dimensions, are about 10 - 20 kpc. 

More information

ING facilities involved:

  • William Herschel Telescope, using auxiliary port CCD
Some references:  
  • Steidel, C. et al, 1995, "Lyman imaging of high redshift galaxies III - New observations of four QSO fields", AJ, 110, 2519



Adaptive optics has again been used on the WHT to obtain distances to the Virgo cluster. A lower limit of 20 Mpc and an upper limit of 55 km s-1Mpc-1. several Cepheid candidates were also discovered and will be monitored.

Researchers obtained CCD photometry of a sample of galaxies to investigate the colours and colour gradients in the bulges. Results indicated that half the bulges an intermediate age population was present.

All three ING telescopes were used to study a recently identified X-ray transient and preliminary results have shown that the compact object could be a black hole with a mass greater than 3.9 solar masses.

The cataclysmic variable UX Uma was observed using the INT Faint Object Spectrograph and results were in qualitative agreement with basic models for accretion disks.

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Last modified: 13 December 2010