scispace - formally typeset
Search or ask a question

Showing papers by "European Southern Observatory published in 1977"


Journal ArticleDOI
TL;DR: In this paper, a photoelectric search is presented for light from a smooth intergalactic background in the Coma cluster of galaxies, and the results show that the light from the background is positively correlated with the brightness of the galaxies.
Abstract: A photoelectric search is presented for light from a smooth intergalactic background in the Coma cluster of galaxies

58 citations


Journal ArticleDOI
TL;DR: The statistics of supernovae (SNe) require unbiased data i n three respects: (I) a complete sample of galaxies that have potentially contributed to the number of observed SNe; (II) a sample of S N e that is representative a n d large enough to give small statistical errors; and (III) good control of the survey times.
Abstract: The statistics of Supernovae (SNe) require unbiased data i n three respects: ( I ) a complete sample of galaxies that have potentially contributed to the number of observed SNe; ( 2 ) a sample of S N e that is representative a n d large enough to give small statistical errors; and (3 ) good control of the survey times. These three requirements can be satisfied only in first approximation. Galaxy samples, even i f distance-limited, are incomplete for dwarfs. Available S N e samples may not be representative because o l the possible bias against S N e in high-absorption or high-surface brightness regions. The number of SNe that can be used for statistical purposes is i n the order of 100, which limits the statistical accuracy to *I0 percent; i f the S N c are further subdivided according to SN type, gal~ixy type, etc., the statistical error can increase to *50 percent or more. Well-controlled survey times are available only for relatively restricted searches that have yielded a fraction of the known SNe; one is forced, therefore, to make certain assumptions about the survey times. These limiting points should be kept in mind for all SNe statistics. A remark may be in place concerning the definition of SNe. Zwicky' has assumed the brightest common novae to reach 1 I\", and he has suggested that all brighter objects be classified as SNe. With the revised Hubble constant of H, = 5 5 km s ' Mpcl (this value is adopted throughout this paper) there is, however, good evidence that all known S N e have been brighter than 15\"' a t maximum.' This brighter luminosity limit avoids the contamination of SN catalogues with variables like V 1 2 in N G C 2403.3 This variable has reached 1 IT3 a t maximum, and its light curve is atypical for a S N . With a limit of 15\"' the case of the highly peculiar variable TJ C a r becomes somewhat ambiguous, because its maximum blue brightness lies somewhere between 14m4 and 17m5.4 This star has remained very bright for centuries and is excluded here. SN 1 9 6 1 ~ . which had an exceptionally slow rise to maximum ( 18m6) for a t least 24 years, is treated here as an unquestioned SN.'.' With this caveat, a maximum brightness of < I 5 \" l is adopted here a s a working definition of SNe .

24 citations


Book ChapterDOI
01 Jan 1977
TL;DR: In this article, the Galactic SN rate is estimated from historical SNe to be τ = 15 (+15, −5) yr. SN frequencies in external galaxies arc determined for a distance-limited subsample of Shapley-Ames galaxies and the frequencies are expressed per unit luminosity for different types of galaxies.
Abstract: The Galactic SN rate is estimated from historical SNe to be τ = 15 (+15, −5) yr. SN frequencies in external galaxies arc determined for a distance-limited subsample of Shapley-Ames galaxies and the frequencies are expressed per unit luminosity for different types of galaxies. It is confirmed that the inclination of (Sc) spirals discriminates against the discovery of SNe. The frequency of Type II SNe correlates well with the galaxy color, whereas the frequency of Type I’s does not. Absolute magnitudes of sample SNe are determined, and SNe in very late-type galaxies are found to be overluminous. The properties and possible precursors of SNe of Type I and II are briefly discussed. Type II belongs to the very young population and Type I to the interarm population. It is speculated that all SNe may lie in close binaries.

18 citations


Journal ArticleDOI
01 Jan 1977-Nature
TL;DR: In this paper, the Coma cluster of galaxies is considered and it is shown that at least 30% of the total luminosity lies outside the regions normally associated with individual galaxies, which can be used to derive restrictions on the nature of the luminous intergalactic material.
Abstract: WE shall turn the simple observation that “there are no intergalactic supernovae” into a quantitative statement for the Coma cluster of galaxies. In this cluster, where at least 30% of the total luminosity lies outside the regions normally associated with individual galaxies1–3, the absence of intergalactic supernovae can be used to derive restrictions on the nature of the luminous intergalactic material, be it a diffuse collection of stars, a background of low surface brightness dwarf galaxies, or some other form of luminous matter.

10 citations



Book ChapterDOI
01 Jan 1977
TL;DR: In this paper, the optical counterpart of the X-ray nova A0620-00 (= V616 Mon) has been made by various observers with different equipment at most stages of its development.
Abstract: Spectroscopic observations of the optical counterpart of the X-ray nova A0620-00 (= V616 Mon) have been made by various observers with different equipment at most stages of its development. Observations in August and September, 1975, show a practically continous spectrum with weak emission lines of He II 4686 and N III 4640, while observations at later stages (early 1976) reveal the spectrum of a cooler source, with absorption lines of He I and possibly Fe II (Chiatti et al., this symposium). These findings agree with photoelectric observations, which show a slow but steady increase in colour index. Unlike in ordinary novae, the brightness increase of V616 Mon can be explained by a temperature increase of parts of the surface of the star, rather than by an increase of surface area from an optically thick expanding envelope.

1 citations


Journal ArticleDOI
01 Sep 1977
TL;DR: In this paper, the main steps of the non-linear theory of spiral structure are described near each of the main resonances, and the sets of non-periodic orbits that follow them are found A different integral of motion is applicable for each set, besides the Jacobi integral.
Abstract: The main steps of the non-linear theory of spiral structure are described Near each of the main resonances the basic periodic orbits are calculated, and the sets of non-periodic orbits that follow them are found A different integral of motion is applicable for each set, besides the Jacobi integral Then the initial distribution function, f, is expressed as a function of the two integrals and the corresponding angles The final distribution function is found by averaging over the angles: Then by integrating over all velocities we find the response density σ resp In order that σ resp should be equal to the imposed density, σ imp we must adjust the parameters of the imposed spiral field The form of σ resp away from resonances can be derived explicitely for tight ana open spirals or bars; however near the resonances σ resp can be only calculated numerically If the imposed field has almost constant amplitude, then the amplitude of the response is very large near the Inner Lindblad Resonance In the case of a tight spiral the azimuth of the response density maximum with respect to the imposed density maximum tends to zero outside the ILR, while it tends to -90° inside the ILR One possible self-consistent solution has zero amplitude inside the ILR both in the case of tight spirals and of bars Finally an important quadrupole term was found near the ILR

Journal ArticleDOI
TL;DR: In this paper, photoelectric UBV sequences were measured in the Small Magellanic Cloud (SMC) and two new photoelectric BV-Skalen were measured.
Abstract: Two new photoelectric UBV sequences were measured in the Small Magellanic Cloud. Furthermore, for some stars of these sequences and three already existing photoelectric BV and UBV sequences we observed V, R and I magnitudes and colours. In der Kleinen Magellanschen Wolke wurden zwei neue photoelektrische UBV-Skalen gemessen. Daruber hinaus wurden fur einen Teil der Sterne dieser beiden Skalen R- und I-Helligkeiten und Farben gemessen. Drei bereits existierende, photoelektrische BV und UBV-Skalen wurden durch V-, R- und I-Messungen erganzt.

Journal ArticleDOI
TL;DR: In this article, the influence of relative motion between a hot star and the surrounding medium on the forbidden lines emission spectrum of the latter is described in an example, where the relative motion of the hot star is considered.
Abstract: The influence of a relative motion between a hot star and the surrounding medium on the forbidden lines emission spectrum of the latter is described in an example.

Journal ArticleDOI
TL;DR: In this article, photoelectric UBV observations of 69 stars, distributed in two sequences north and south of the galactic star cluster NGC 5823, are reported, and two lichtelektrisch beobachtete UbV-Sequenzen, nordlich und sudlich des offenen Sternhaufens NGC5823, angegeben.
Abstract: Photoelectric UBV observations of 69 stars, distributed in two sequences north and south of the galactic star cluster NGC 5823, are reported. Es werden die Daten fur zwei lichtelektrisch beobachtete UBV-Sequenzen, nordlich und sudlich des offenen Sternhaufens NGC 5823, angegeben. Die 69 Sterne der beiden Sequenzen uberdecken den Helligkeitsbereich V = 9m·5 bis V = 15m·9.