INTRODUCTION
Early Astronomical Works on Southern Double Stars
Historically, many of the very brightest and
well known southern pairs below declinations of around
−30° were first located by accident. These were more often
found by travelling astronomers while visiting low northern
latitudes. Some during the 15th Century, being relatively unknown
amateur telescopic observers, who had already revealed the bright
double stars of Alpha Centauri and Alpha Crucis, just by casually
gazing towards the southern skies. For example, the Jesuit priest,
Father Ricard, discovered the duplicity of
α Centauri in 1689 AD when observing
from the ancient city of Ponicherry (now Punucherry), located on the
east coast of Southern India. In 1685, was the discovery of α Crucis by another Jesuit priest named
Father Fontenay from Siam (now Thailand). Regardless, these pairs
remained astronomical curiosities.
First of the multiple discoveries of the widest of
double stars were taken from the 9,776 southern star catalogue by
French astronomer,(Abbe) Nicolas-Lois de a Lacaillé
(1713-1762), who made his observations from the Cape of Good Hope
between 1751 and 1753. Using only his very modest ½-inch
(12.5mm) telescope, Lacaillé produce the first truly southern
catalogue of stars, whose general comments contained rudimentary
information on several wide pairs that he had found.
Few of these pairs are recognised today. Only two
remain in the recent version of the Washington Double Star Catalogue
(WDS07). First is the multiple star β1, β2 Tuc / LCL 119 /
Beta (1,2) Tucanae (00315-6258), being widely separated by 174
arcsec. Another is the faint yellow pair, LCL 120 AB
(04038-4429), of 8.6v and 9.6v magnitude and separated by some 80
arcsec. Perhaps the most prominent of Lacaillé discoveries is
the optical pair δ1,
δ2 Aps / Delta (1,2)
Apodis, now listed as the double star, BSO 22 (16023-7842).
BSO 22 has components of 4.9v and 5.4v magnitude and are currently
103 arcsec (1999), whose separation in continuing to widen.
Discovery of the Dunlop Pairs
When Dunlop started his own observations of
doubles star in 1826-1828, little was know the extent nor numbers of
southern systems. Comparatively speaking, in the northern skies the
number and quality of observations made by similar observers had been
improving significantly. You have only to compare the work of likely
the greatest double star observe of all, Frederick Wilhelm
Struve (1793-1864), who was observed about the same time as
Dunlop. Struve’s brilliant double star
career began in 1814, whose first published double star catalogue in
1822 contained some 795 new systems, Later, using the sizeable
quality 24.5cm (9.6-inch) Fraunhofer refractor at the Russian
observatory in Dorpat, he undertook the methodical discovery and
started measuring double with a very high-quality filar micrometer.
Struve found more than 3,000
‘Σ’
pairs, with the main catalogue published in 1837. After this, Struve
continued to repeatedly measured most of the other then known
northern pairs.
In comparison to this story, observations made by
James Dunlop just seem an incompetent work and quite amateurish.
During the 1820s, the southern skies below about −30°
declination were literally the ‘virgin
frontier’. In the annals of history the
works of Dunlop and Rümker marks only the first initial survey.
Historically we have held in the wider astronomical community the
persistent story that has much maligned and berated James Dunlop.
They openly criticise his first catalogues, claiming that most
objects were imaginary or even optical mirages from his poorly made
equipment. Another common slight is that the many poorly obtained
positions of all his objects contained too many avoidable errors. In
regards his double star measures, many still deem these observations
of little consequence — mainly because they are generally wide
and likely most are only optical pairs.
Although some of the negative views maybe true, the reasoning
behind his presumed weaknesses could be simply argued because of
Dunlop’s isolation away from his peers
and the rest of the astronomical community in both England and
Europe. With the new colony of New South Wales several months away by
ship, communication was very difficult and slow. A simple question or
advisement could take three to five months to answer. At first, the
new discoveries received many accolades. Yet, when other observers
re-examined his discoveries, their great elation soon turns to real
disappointment and honest hostile criticism.
Importantly, the key issue with our judgements is that Dunlop
never did claim that his observations were either perfect nor very
exacting. Creating his new double star list was made under the very
least favourable conditions, often when atmospheric seeing
was poor or when the Moon was near full, whose general timing was
when deep-sky observing or measuring stellar astrometric positions
was nearly impossible. For Dunlop, there could be no opportunity of
clear skies to be lost. Moreover, he allegedly did all this work in
just fractional over a single year. (There remain some disagreement
with this later point, because the list of doubles may span back to
1822 when the observervations of the Paramatta Star Catalogue
was being made.)
The Demeanours of Rümker and Dunlop
At the very start, likely from their first meeting, Charles
Rümker and James Dunlop were never friends. Whilst in Australia
they were really acquaintances and barely tolerated each other
— forced together as astronomical coworkers. When they spoke
to other people of the other’s
attributes or abilities, they were sometimes expressed in quite
derogatory terms. At times their open hostility caused several
problems with the Colonial Government, requiring in one or two cases,
intervention to settle issues with withholding of vital observations.
After the sudden departure of Sir Thomas Brisbane in December 1825,
who had been the sole financier and subsequent driver of the
observational projects at Paramatta Observatory, these issues came to
a head — especially in who should be chosen to supervise and
run the Observatory. Several times, they openly rebelled against the
Governmental decisions, and they clearly refused to work together.
Both were so forthright and stubborn, that they were quite
unashamedly quite happy to sacrifice everything — so, at
different times, they preferred to leave Paramatta Observatory
altogether for several years instead of collaborating.
The origin for these dramas were probably their
quite different professions and personalities.
PROFESSIONALLY
Rümker was mostly the consummate
astronomer. He had a very firm grasp of astronomy, navigation and
celestial mechanics; along with the underlying mathematical skills.
From the very beginning, his appointed position by Brisbane was as
his First Assistant. His main task was intended to do all the
mathematical reductions of the transit or mural circle observations
for the Paramatta Star Catalogue. For this reason, he
deservedly received the higher and sizeable £200 salary.
Dunlop had no real astronomical qualifications
but was the keen visual observer, which Brisbane clearly appreciated
and openly encouraged. He was hired as the Second Assistant,
being very practical, mechanically capable, doing various repairs or
making basic instruments if and when such tasks were required. He
could also adapt readily to new situations. Dunlop was mostly hired
to make all the necessary stellar transit or mural circle
observations.
PERSONALITIES
Rümker moody and difficult, and this was
probably the main cause of the angst between him and both Dunlop and
Brisbane. His character and personality appears to have been quite
abrasive and he was often condescending to others. His stricter
background, combined with his thick German accent, may have
contributed much towards their perceived differences.
Dunlop is often portrayed as being far more
friendly and cordial, but he too could be difficult and abrupt. Upon
the arrival in the Colony of New South Wales, little trouble is said,
but right uptil the time Rümker left the observatory in 1823,
small cracks of discontent appear. Commentators on Dunlop are
uncertain why this happened, but it was seemingly either due to
illnesses or troubles with the various bureaucratic decisions that
affected his life after Brisbane’
removal as N.S.W. Governor. These stated discrepancies are
historically intriguing, and future investigation may bring us closer
to the truth.
Consequences From Their Actions
For whatever reason, the personalities and portrayed behaviours
between Dunlop and Rümker was to place them both diametrically
on opposite sides. Most of the merge literature about them, seems to
suggest this is likely scenario that explains their many astronomical
shortcomings and failures in New South Wales. It is not unreasonable
to conclude that Dunlop’s shared
Scottish heritage with Brisbane, made Rümker to be the ‘odd man out’.
I am still unsure if Rümker personally did feel indignation or
bitterness against them, but he was certainly more resentful of the
strong long-term friendship and open camaraderie between the two
Scots. There is no doubt that much the friction was exacerbated by
differences in their personalities or their differing cultures and
heritage. It is quite reasonable to believe this to be true.
In the end, this clash meant they were not being able to working
together to produce double star and deep-sky probably irreparably
damaged both of them. Had they contributed their skills towards their
common cause, the story of the astronomical exploration of the
southern skies would probably have been somewhat different and even
more complete. Unfortunately, this was not to be, and the kudos and
honour for this was to be taken by John Herschel in South Africa
almost ten years later.
Comparing the Double Star Catalogues of Rümker and
Dunlop
As we have said previously, large proportions of the Dunlop pairs
are usually wide to ultra-wide. As the probability that two randomly
selected stars in proximity are associated decreases with apparent
distance, therefore, the natural conclusion will deem such pairs as
less important. Moreover, even if both stars were physically joined
by gravitation, it would still take many centuries before this could
be ascertained. Indeed many of the later criticisms levelled against
reputation of Dunlop stem for the huge broadness of his selection of
pairs. The other is the very high proportion of missing pairs. Here
only 165 of 253 stars (65%) are real pairs, with three
being duplicates of multiple stars. I.e. γ Velorum (Δ64,Δ65),
u Car (Δ102,Δ103) α1,2 Crucis (Δ122,Δ123). In the published catalogue,
thirty-two (32) were rediscoveries of previously known pairs,
thirty (30) being unknown or lost doubles, with
twenty-two (22) remaining uncertain with their identification.
One star was not even double star being the variable star, R Scl as
Δ3 !
Rümker instead has the better reputation, due to many of his
pairs are closer together in separation and as they have better
chances of being binaries. Today, and perhaps likely unfairly, his
double stars remains much higher in importance than those of Dunlop.
Rümker found only twenty-eight (28) pairs with
sixteen (16) (57%) donned as real discoveries by him. Only
five (5) of these were discovered earlier by Dunlop.
I.e. RMK 1, 5, 6, 7 and 21. Another seven (7) are either
missing, wrongly identified, or are single stars.
It is interesting why people continue to have this wayward
impression that Dunlop was a poor observer but Rümker was
better. For me, after looking the latest Washington Double Star
Catalogue (WDS11) data, we have observed many of his pairs though
there are fewer measures — at least when compared other
more southern ‘valued pairs’. Perhaps we have continued to wrongly
interpret our perspective on the achievements of these two double
star catalogues. Observationally, and in the light of what was to
come, BOTH Dunlop and Rümker reputations should be
somewhat tarnished!
No doubt, the start of degradation against these observers began
when the eminent John Herschel started his southern observations that
aimed to join his father’s earlier
northern work into the first all-sky survey of double stars and
deep-sky objects. Between 1834 and 1838, John Herschel found over two
thousand new pairs, and measured many of them. In addition, John
Herschel found nearly all of the errors in the Dunlop double star
catalogue.
Upon Herschel producing his own privately funded
book and catalogue in 1847, more criticism started to rapidly mount
against Dunlop — inferring that he was essentially a poor and
unreliable observer. This general reputation stuck, and is still
even touted today.
Yet is this view truly justified?
For me it all depends on how you look at his double star
catalogue. If you look at it from the perspective of an initial
survey then what he has produced really just lays down the
groundwork for the other surveys. John Herschel found much promise in
the observations of Dunlop, and began to advocate for Dunlop in his
isolated position. While John Herschel was still in England, he
keenly read Dunlop’s deep-sky and
double star work with great interest and enthusiasm. Herschel,
however, was concerned with Dunlop’s
general presentation, and so he reorganised the observations for
publication. This finished paper was soon completed and read on 9th
May 1828 to the Royal Society. Entitled “XVII. Approximate Places of Double Stars
in the Southern Hemisphere, observed at Paramatta in New South
Wales.” Mem.Ast.Soc. London, 3, 257;
(1829).
Dunlop himself places the assessment on the merits of his own
manuscript;
“In presenting this
list of double stars, it may be necessary for me to make some apology
for its imperfect state, as regards the true and apparent distance
and position of a great many double stars, the situation of which
points out in the heavens.”
Dunlop is not really being just humble here. It is likely Dunlop
honestly is concerned with the observations and clearly states the
nature of his own programme. For Dunlop the statement “nebulae being a prime object to
me”; proves his main observational goals towards his
endeavours. He affirms this by saying the deep-sky observations were;
“devoted the whole of the
favourable weather.” It seems the collection of double
stars were only of secondary importance and many of then were likely
found while doing his deep-sky surveys. It is likely that he observed
the pairs again when the next opportunity came along under these
poorer conditions. I.e. Observing in moonlight or during poor seeing
— the latter condition beings the worst time to observe pairs.
By observing during bad seeing this might account for many of the
missed close pairs.
In the scheme of things Dunlop and Rümker’s observations maybe of little consequence
but they did lay the foundations of later surveys by other
astronomical “heavyweights”. For
me we should perceive Dunlop, and Rümker to a lesser extent, as
the ones who opened the celestial door into the observational
southern skies. It was everyone else who later found the nature of
the treasures contained within and gathered its rich harvest. As for
opening this part of the celestial vault — for this alone we
should be eternally grateful.
Dunlop’s Other Astronomical
Works
James Dunlop made observations of other astronomical phenomena.
One of the most important was observing Encke’s Comet. He measured the position of the
comet some thirty times between October 26 and December 26 1828, and
reduced the cometary positions when he returning to Brisbane’s Observatory at Makerstown in
Roxburghshire. (MNRAS, 1, 120 (1829))
Other than double stars, nebulae and clusters in the southern
skies, Dunlop also produced a paper himself on stars entitled “IV. Observations of the Magnitude,
Colour, and Brightness of Stars in the Southern Hemisphere.”; MNRAS, 2, 190 (1830) This
little examined document contains information on some 400 southern
stars under headings of magnitude, lustre and colour. Stellar
magnitudes were measured by means of the ‘double eyepiece’, where relative telescopic magnitudes and
colours are determined by sizes of artificial bright disks. The
original submitted paper is now currently available in the R.A.S.
Library in London.
Also closely examined were the comparisons between “neighbouring stars”, in the hope, in Dunlop’s words, of “...enabling observers to discover any
changes that may hereafter occur.”
This project was an additional to the observations for the main
positional catalogue of southern stars in the ‘Paramatta Catalogue of Stars’.
The Paramatta Catalogue was the second specific dedicated
positional star catalogue made from the southern hemisphere. French
astronomer, (Abbe) Nicolas-Lois de a Lacaillé
(1713-1762) created the first catalogue, making extensive
observations between 1751 and 1753 from the Cape of Good Hope. This
published work in its partial form appeared in ‘Histoire Céleste
Française&rsquo as the ‘Caelum
Australe Stelliferum’ or ‘Coe Australe’
catalogue in 1763. It contains in total some 9,776 stars made within
the very short time of eleven (11) months using only a small
equatorial mounted 1.3cm. (½-inch) refractor.
This star catalogue was mainly of the naked-eye stars and many 7th
and 8th but the positions certainly were not sufficiently accurate
for astronomical purpose such as proper motions. A further completed
reduction appeared in 1847.
Dunlop used much of this catalogue that was going to become the
basis of the Paramatta Catalogue, which has many of his stars appear
listed through its pages. He also partial examined the errors of
Lacaillé. Whilst doing this star catalogue, Lacaillé
had discovered and catalogued forty-two (42) nebulae and
clusters that was first published as “Sur les étoiles nébuleuses
du ciel austral”; Mémoires
de l’Académie Royale des
Sciences (1755). Of these some thirty-four (34) are actual known
objects, some twenty-six (26) being Lacaillé’s own discoveries.
According to the Paramatta Star Catalogue, observations began in
November 1821 and finished on 2nd May 1822. After June 1823, Brisbane
made only a few further observations, with the majority of visual
observations and measurements now obtained by Dunlop, and to a lesser
extent by Rümker. Other separate positional observations
specifically made for the British Admiralty occurred between the 2nd
May 1822 and 2nd March 1826, and the results returned to England
during 1829 and also into 1830. The catalogue results were soon
followed, where Mr. William Richardson was duly employed by the “Lord Commissions of the Admiralty”, who then was directed to re-reduce all the
observations.
Mural Circle observations of all these visual stars were computed
for the latitude of −33° 48′ 50.685″. This
was before Rümker had formally determined and published the
observatory’s longitude in
“Philosophical
Transactions” Hamburg (1832) for epoch
1829, as 10h 04m 06.25s E of Greenwich. The Observatory height he
also estimated as 60-feet.
Richardson says that the Paramatta Catalogue is a “Catalogue of Southern Stars, as far as
8th magnitude.” He goes on to
say;
“During the greater
part of the time embraced by the Paramatta observations, Mr. Dunlop
was the only observer; and with the point of view the complete
observations for the formation of an extensive catalogue, he
abandoned the transit instrument, and fixed the Mural Circle as
nearly to the meridian as he could, he commenced observing every star
that circumstances permitted as it passed the central wire, regarding
the time of transit, and read off as many microscopes as the interval
before another object came to the wire would allow.”
Richardson goes on to state;
“In a period of about
two years and a quarter… he observed 7,000 stars, and made
nearly 40,000 observations, besides as extensive series of
observations upon double stars and nebulae.”
James Dunlop’s main problem was
having a variety of astronomical equipment for use, which was only in
reasonable condition. It seems probable that both the main
measurement devices; the Transit Telescope and Mural Circle may have
been permanently damaged during long transport by ship from England
to Australia, while being delivered to the Paramatta site or when
being set-up for use. We know this from the problems faced when
determining observations and the general poorness of the data seen in
Paramatta Star Catalogue — importantly as something that cannot
be solely be blamed just on the observers! Both Dunlop and
Rümker attempted several times to determined some kind of
correction to the instrumental error, but we know it was only
partially successful. The final catalogue data never implemented many
of these corrections.
At Paramatta Observatory, Brisbane transported to Australia an
accurate clock made by Hardy that showed local sidereal time. This
first exclusively used in conjunction with the principle positional
equipment being the 16-inch repeat circle, and both the Troughton
5½-foot transit telescope and 2-foot Mural Circle. The Transit
circle when installed caused many serious positional problems in the
PSC catalogue, so Dunlop alone made the critical decision to do star
transit observations using the less precise Mural Circle. This choice
was to have serious consequences on the questionable quality of the
final star catalogue. All these instruments were place in solid
masonry at the observatory site.
Once Paramatta Observatory was finally demolished, the the powers
that be just stored all the astronomical equipment for safe keeping.
Around this time, many of the smaller parts of the equipment went
missing — being the important pieces making the instruments
quite unusable. When Sydney Observatory was first finished in June
1858, the exhumed equipment went there, but never used really used
again, except for the clocks. This equipment remained there until the
closure of the functioning Observatory in 1983. After this, all the
equipment was removed to be properly cleaned, restored or revamped by
the Sydney Powerhouse Museum. Now most of it is on the Sydney
Observatory site under glass displays as part of the interesting
historical exhibits. Some still remains away from the public to be
perhaps rotated over the years for public display.
James Dunlop’s Catalogue of
Deep-Sky Objects
In the years 1823-1827, James Dunlop (1795-1848) observed the
southern skies from the Brisbane observatory at Paramatta, New South
Wales, Australia. He compiled several catalogues, among them the
Brisbane Catalogue of over 7,000 southern stars, and “A Catalogue of Nebulae and Clusters of
Stars in the Southern Hemisphere observed in New South Wales of 629
entries for deep-sky objects” [Dunlop (1828)]. John
Herschel, however, could only verify 211 of them, mainly due to wrong
positions or poor contrived descriptions. Recent research, led by
Glen Cozens, brought up the number of further ‘real’ objects,
so that actually roughly over three hundred (300) (or about
50%) seem to belong to real deep-sky objects. It seems the other half
found by Dunlop are asterisms and multiple stars, most found with the
comparatively small instruments but he did not resolve them. His main
telescope was homemade reflector, being the 9-inch speculum metal
mirror of 9-foot focal length. This he used for all the other
observations that were roughly mounted on an altazimuth mount aligned
along the meridian. As a telescope, it was perhaps equivalent to some
modern 6-inch reflector, though the images produced we quite poor. A
small selection of eyepiece optics was crude at best, and it seems
likely that the high-powered eyepieces were almost unusable.
Perhaps, the most spectacular original discovery he catalogued was
the peculiar radio galaxy NGC 5128 or Centaurus A in
Centaurus, (Δ482.) Original
discoveries also included the Sculptor Group galaxies; NGC 55
or Δ507, NGC 300 or Δ530, and NGC 7793 or Δ608. Others included considerable numbers
of other southern galaxies, open and globular clusters, and diffuse
nebulae.
Four (4) discovered planetary nebulae included; NGC 2818 or
Δ564, NGC 5189 or Δ252, NGC 5882 or Δ447, and NGC 6563 or Δ606.
Dunlop has included six
Messier objects in his list. These include; M54 or Δ624, M55 or Δ620, M62 or Δ627, M69 or Δ613, M70 or Δ614, and M83 or Δ628.
Arrangement of the Dunlop catalogue is in order of increasing
declination or south polar distance, from south to north. Objects
nearest to the South Celestial Pole come first, and also explains the
late numbering of the comparatively more northern Messier objects; ;
M83 is the brightest and one of the northernmost of all the Dunlop
objects. This endeavour was the second major effort of a deep-sky
object survey of the southern skies, after Lacaillé’s list of 42, of 1751-1752.
First used by John Herschel was the exclusive symbol of ‘Δ’ for all the Dunlop deep-sky and double
stars, whose use continues today. This can be sometimes confusing
between the deep-sky objects and multiples. In the Washington Double
Star Catalogue or WDS, the designation for Dunlop pairs is ‘DUN’. It is
preferable to use these designations, though more often than not they
are commonly interchangeable with authors and among amateurs.
ASTRONOMICAL PAPERS of JAMES DUNLOP
- Dunlop, J.; “A Catalogue of
Nebulae and Clusters of Stars in the Southern Hemisphere observed in
New South Wales.” Phil.Trans.Royal.Soc., 118,
113-151 (1828)
- Dunlop, J.; “Dunlops
Verzeichniéon Doppelsternen AN., 7, 113
(1829)
- Dunlop, J.; “Places of
Encke’s comet, from 30
observations.” MNRAS.,
1, 120 (1829)
- Dunlop, J.; “XVII. Approximate
Places of Double Stars in the Southern Hemisphere, observed at
Paramatta in New South Wales.” Mem.Ast.Soc. London,
3, 257; (1829)
[Ref 1.]
- Dunlop, J.; “ Observation of a
small comet at Paramatta.”
MNRAS., 1, 130 (1829)
- Dunlop, J.; “Observations of the
Magnitude and Colour, and Brightness of the Stars in the Southern
Hemisphere.”; MNRAS.,
2, 190 (1833)
- Dunlop, J.; “Observation of
moon-culminating stars, eclipses of Jupiter’s satellites, and occultations of
stars.”; MNRAS, 5, 8
(1839)
SHORT NOTES on PAPER No.6.: James
Dunlop presented a short paper to the RAS in 1833, which estimated
brightnesses of some 400 southern stars using a double-image
eyepiece. This made artificial stars into disks where the magnitude
was determined proportional to known magnitude stars. Dunlop also
listed their lustre and colour. His aim in the presentation of data
was to discover any changes in the future and the discovery of any
secular variables. After the great brightness changes seen in the
star of Eta Argûs, now called Eta Carinae,
southern observers thought that several other star might be similarly
variable. Unfortunately, this paper is not available and appears only
as an abstract summary. It is likely still somewhere in the Royal
Astronomical Library (RAS) in London, but based on the methodology
this paper is certainly quite flawed. Some of these observations
do appear within his unpublished manuscript.
Last Update : 24th April 2016
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