INTRODUCTION.
This presentation consists of a complete survey of all IC identities supposed to
be galaxies found throughout both the northern and southern celestial hemispheres.
Its purpose is firstly an attempt to determine the correct type of the objects
involved and which of the identities are truly galaxies and which are either
single or multiple stars or nonexistent and secondly, to correlate the data
published in a number of the most quoted modern sources, primarily catalogues
which list such identities, in order to evaluate any apparent ambiguous
information they might contain.
IC galaxies as a whole have never received the same amount of attention given to
those identified as NGC galaxies. This is true in both the professional and
amateur world of astronomy. The reasons for this are easily understandable due to
the fact that as generally the images of IC galaxies are both fainter and smaller
than most of those having NGC identities, a function of distance in the majority
of cases, the professionals have naturally preferred to conduct their studies of
the brighter and closer NGC galaxies, unless for some reason a particular IC
galaxy exhibited unusual properties.
For the amateur the reasons are somewhat similar in that until fairly recently
telescopes of apertures larger than 31 cm were not common and this restricted any
extensive observations of the IC galaxies, however, in recent years the vast
increase in the use of telescopes of larger aperture and the even more recent
availability of CCD camera systems now allows the amateurs the challenge to expand
their observing programmes to include many of the IC galaxies.
Because of such a lack of previous attention the majority of the IC identified
galaxies have not been examined since they were originally discovered between the
years 1888 and 1908 and therefore it has not been clearly established whether all
such identities are valid as nonstellar objects. Indeed even for the relatively
few IC galaxy identities found in many of the modern catalogues the diversity of
opinions as to their character or type is extensive, some catalogues listing a
particular IC identity as being a galaxy while another catalogue describes this
same identity as being a single or double star.
It is the author's intention to attempt to carry out this survey of all IC galaxy
identities by employing the original observational data published in the lists of
the discoverers and evaluating this data by examination of the Palomar Observatory
Sky Survey Prints (1954) and Digitized Sky Survey (DSS), in order to determine
just exactly what it was they had observed as it is solely dependent upon their
observations that Dreyer designated the IC identities.
The survey was begun in early 1992 after I had received a computer printout of the
1950 coordinates of all the IC galaxies north of declination -28 degrees, kindly
supplied to me by Dr.A.C.Davenhall of the Astronomy & Physics Department of
Leicester University, England. (Presently at the Royal Observatory. Edinburgh).
These coordinates had been precessed from the data given in the NGC 2000 (1980) in
order to accommodate my decision to base all of my investigations upon the epoch
1950 as the majority of the modern catalogues that were to be included in my
research, CGCG, MCG, UGC, MOL, DSFG, PGC and RC3 provide coordinates for this
epoch. Additionally I included in my study those references to galaxies in two
major published papers dealing with errors and omissions (D.CARLSON. 1940) and (G.
PATUREL. 1991), in which they had determined discrepancies existed in various
catalogues. Also I have included references to two lists by Dr. Harold G. Corwin,
THE ACCURATE POSITIONS LIST and NGC/IC BUG LIST. Also I have compared Wolfgang
Steinicke's excellent REVISED NEW GENERAL CATALOGUE AND INDEX CATALOGUE (March 31st
2005) for this version of my survey.
This then has required examination of all the IC identities which would be
classified in the galaxy category and it is my opinion that about one-third of
these have errors, omissions or other related inconsistencies in either some of
the historical or modern literature and it is these ambiguities that are addressed
in this presentation.
THE SURVEY METHODOLOGY.
Initially the survey was begun by resorting to SELECTED AREAS, this being
determined by the 100 Palomar prints in my own collection. Each of these prints
were examined for every IC identified galaxy contained within their 6.5 X 6.5
degrees of field and the results compared with the historical and modern identity
data. At the completion of this SELECTED AREAS phase I continued the remainder of
the survey using the full set of Palomar prints which were made available to me at
the Instituto de Astronomia in Ensenada, Mexico.
The survey was now carried out by ZONES OF DECLINATION, beginning with the 10
degrees lying between the declination zones +90 and +80 and examining all IC
identified galaxies listed in the NGC 2000 as existing between 00hr and the 24th
hour of RA . After completing this zone I repeated the same procedure in the next
10 degree zone lying between + 80 and + 70 and this same procedure was continued
throughout in increments of 10 degrees in declination, the only exceptions being
for those regions already covered in the SELECTED AREAS.
In early 1997 I returned to California from Mexico and continued the study using
the Digitized Sky Survey on the Internet from which to search for and examine the
photographic images of each of the IC identities not previously covered.
Having decided to conduct the survey by using only the data published in the
actual lists compiled by the individual discoverers I employed as reference
objects only those stars either used by the discoverers in their observations, or
in the cases where they did not indicate reference field stars I used GC stars
(BOSS. 1936) or GSC stars and from these measured the necessary separation values
needed to locate the positions where the different observers had indicated they
had found their credited IC objects. This then made it necessary that I obtain a
large number of out of print historical sources and the success for achieving much
of this I owe to my good friend Steve Gottlieb who in response to my many requests
searched the records of various academic institutions and located for me copies of
much of the materials I sought.
This original observational data provided the major basis for my evaluations and
without them many of the solutions to a large number of the errors I encountered
would not have been possible, as regardless of what constituted the error the
original IC identity had been assigned due to these historical observations.
As a result of having examined these historical observations it has become quite
obvious to me why many of the errors of identity found in the modern catalogues
can be attributed to their compilers not having consulted such original sources.
This is particularly true in those cases involving equivalent identities in which
the modern data makes one identity equal to another. Careful study and
comparison of the data in the discoverer's observations often reveal that such
equivalency is incorrect and that there was absolutely no possibility that the
original discoverer was ever confused, causing him to claim as a nova some other
adjacent object.
In an attempt to establish correctly those identities which might appear doubtful
I also measured separation values from a number of associated field galaxies using
only those coordinates which had been given by the discoverer in order to allow
for any possible slight positional bias on the part of the discoverer.
Many of the IC identities have extremely compact images making it at times very
difficult to accurately determine whether the image is nonstellar or that of a
faint star. There can be little doubt that many such images are indeed those of
stars which at the time of their discovery suggested being nebular. This is by
no means restricted to those discovered visually as it is apparent that a large
number of such misconceptions are the result of discovery by examination of early
long exposure photography e.g. Schwassmann and Wolf, although it must be pointed
out that in many such cases the discoverer suspected that the object he had listed
was perhaps only a star, referring to this possibility in his descriptions. When
it became impossible for me to make a definite decision as to a stellar-like image
I have listed it as "Unable to confirm" although I suspect in a majority of cases
such a definition does refer to a faint star.
Some of the IC identities I searched for produced no candidates that could be
considered suitable, due primarily to the nearest nonstellar images being at a
distance too far from the given coordinates.
Generally speaking I found that overall the historical positions for the IC
galaxies were superior in accuracy when compared to many originally published for
the NGC galaxies, regardless of whether they were made visually or determined from
photographs, therefore I was more reluctant to allow for accepting possible
candidates with positions not in keeping with the original coordinates unless
other convincing factors were present. Instead I listed such missing identities
as "Not Found".
The reasons for these "missing identities" I believe are due to either optical
problems such as stray light entering the focal path of the telescope, or small
misalignment in the telescope's optics causing spurious images to be mistaken for
nonstellar ones. Certainly Bigourdan (1919) experienced such phenomenon, e.g. IC
640 and IC 641, in which he thought in his first observation of the field that
they were two nebulae, however, almost 20 years later he re-examined the same
field and found no such objects and decided that his original assessment had been
caused by "false images." Such spurious images may also account for the
nonexistent identities listed from photographic discovery and can often be the
result of defects on the plates caused by photographic procedures or the chemicals
employed.
It is the hope of the author that this survey will help somewhat as a small
contribution to the accuracy of identities in future astronomical literature.
Although I am aware that some critics consider the whole idea of historical
identity not of any importance, stating that most present day professional
astronomers could care less about this, I can only respond by saying that as long
as these same professionals continue to produce papers using such identities and
compilers of catalogues continue to employ the historical designations in their
catalogues they should at least when possible get the identity correct.
I wish to make it quite clear that except in those few cases in which large errors
of coordinates were discovered and which provided pronounced effects upon the
identities of the involved galaxies I attempted to not became embroiled in trying
to attain corrections to the almost universally small differences accorded to the
published coordinates of galaxies as found in all the major catalogues. These
differences result in most cases from the personal evaluation bias of the
individual measurer and differences of up to as much as 18 seconds of RA, or 3 to
4 minutes of arc declination are often found to exist between the compilers of
such catalogues, even when it is absolutely positive that each are referring to
exactly the same galaxy.
The two sets of coordinates (1950 and 2000), I show immediately following the
discoverer's name and Object numbers was arrived at by employing the excellent
tool, COORDINATE AND EXTINCTION CALACULATOR, recently provided by NED---NASA
EXTRAGALACTIC DATABASE, which allows the user to input coordinates for any year
and receive in output the accurate coordinates for any other year, in my case for
the years 1950 and 2000. Thus the coordinates I list are NOMINAL positions based
entirely on those as given in the published lists of the discoverers. Therefore
it is very important that the reader be completely aware that these positions will
reflect errors varying from small to large, dependent upon the original accuracy
as provided by the discoverer. Those wishing accurate coordinates for where the
identified galaxies are to be found should consult the IC Files of either Dr.
Harold Corwin or Wolfgang Steinicke.
NOTE: For a detailed explanation of the NOMINAL POSITIONS, (Nominal and Corrected
Nominal) I have employed for this survey the reader should consult EXPLANATION OF
SURVEY RESULTS.
THE HISTORICAL DATA.
The two publications known as the INDEX CATALOGUES or IC I (Dreyer 1895) and IC II
(Dreyer 1908) were designed as supplements or indexes to the famous NEW GENERAL
CATALOGUE or NGC (Dreyer 1888). These two supplements contain a total of 5,386
identities considered to have been discovered between the years 1888 and 1908.
Although a few of the discoverers from the NGC also provided objects for the IC
catalogues the majority of the IC objects were the result of contributions from
Bigourdan, Swift, Javelle, Wolf, Schwassmann, Frost and Stewart.
As it may be of some interest to the reader I have included the following
background information on these seven observers and their lists of discovery.
LEWIS SWIFT :
Lewis Swift it would appear had no professional training in astronomy, however,
what he may have lacked in academic requirements he more than made up for in an
interest and obvious love for deep sky observing. He acquired the use of a fine
16 inch refractor at Warner Observatory in Rochester, New York; where he conducted
visual observations which produced in two years about 600 new objects which were
incorporated into the NGC and were also published in six separate lists in the
ASTRONOMISCHE NACHRICTEN.
Swift has been considered somewhat of a character by many and it is true that his
methods for obtaining positions for his discoveries are rather less than perfect.
Although over sixty years of age when he began discovering nebulae, he determined
coordinates by putting the object in the centre of the large field of view
provided by the eyepiece he employed, a Gundlach giving a 32 arcminute field with
a magnifying power of 132x, and then climbing down from his observing ladder and
reading directly from the telescope's setting circles. (This information provided
in a letter from Dr. H. Corwin).
Due to Swift's many positional errors investigators often experience difficulty
confirming his identities, however, with a little patience and some luck one can
generally obtain sufficient data from his descriptions to be able in the majority
of cases arrive at reasonably sound conclusions, especially by using the
information given in the A.N. which often is more detailed than that given in the
NGC and IC catalogues, however, it must be cautioned that due to the large number
of poorly given coordinates furnished by Swift in his published lists it becomes
somewhat difficult to identify some of his claimed nonstellar identities as being
single or double stars based solely upon the fact that that is what one finds at
his given positions, as such positions may be subject to large errors in
themselves and therefore when only stellar images are found at his nominal
positions one should perhaps not immediately assume that such images are what he
was actually referring to as his specified discovery. In such cases I personally
feel that they should be termed as "Not found.".
Beginning with his List # 7 Swift's discoveries are primarily for IC identities
and Swift's Lists 11 and 12 deal mainly with Southern Nebulae discovered at Lowe
Mountain, Southern California where he had re-located the 16 inch refractor and
Swift used this 16 inch refractor for visual observations between the years 1895
and 1898.
In the case of Swift's visual observations for his Lists XI and XII it must be
taken into account that many of his claimed IC identities would have been at
extremely southern declinations when viewed from his location.
Almost all of those that can be confirmed are as would be expected quite bright
objects, usually 13 Mv or brighter, therefore suggested candidates of 15 and 16 Mp
must be subject to a large amount of caution unless they meet other requirements
such as descriptions of associated stars etc.
Additionally, in these two lists Swift appears to have had problems with his
chronometer, or setting circle readings as most of his RA errors are off by being
too small in value and although there are exceptions I would say that his errors
are usually more in one coordinate, either RA or Declination, not both.
Swift's observational lists No. 1 through No. 6 have coordinates based upon epoch
1885, while Lists No. 7 through No.10 are for epoch 1890 and his No. 11 and No.12
are based on epoch 1900. He began his observations in April of 1883 and his last
observation is dated November 19th, 1898. His coordinates are given in hours,
minutes and seconds of RA throughout his twelve lists, however, although his
declinations were given to the nearest second of arc for his first seven lists the
remaining five lists were given only to tenths of an arcminute. Descriptions are
in the letter form as found in the NGC and IC catalogues, but there are for many
of the objects he observed considerably more information than Dreyer gives, with
numerous references to other stars or groupings of stars visible in the 32' field
he employed. At the end of many of his lists Swift included a Notes section where
he gives additional information pertaining to specific objects he had discovered.
Additionally, Swift published a series of SHORT LISTS in various sources such as
THE ASTRONOMICAL JOURNAL, MNRAS, POPULAR ASTRONOMY and PASP. These deal mainly
with his southern discoveries and were later combined into Lists XI and XII
ASTRONOMISCHE NACHRICHTEN.
Regardless of his observing procedures he should be admired for his love of
observational work and with almost 1200 NGC and IC objects credited to his name he
surely deserves to be recognized as an observer in the true amateur understanding
of the term.
GUILLAUME BIGOURDAN :
This French astronomer certainly deserves the esteem that is associated with his
ability as a highly skilled observer. His visual observations with the
exceptionally fine 310 mm equatorial refractor of the Paris Observatory over a
period of more than twenty years were published in a monumental work (Observations
De Nébuleuses Et D'Amas Stellaires. 1919) and detail his survey of almost all of
the NGC objects visible from his latitude and also includes the hundreds of Novae
he discovered and which received IC identities from Dreyer.
Bigourdan must have possessed extremely sharp visual acuity as often when I
examine images on the Palomar prints that are credited to him I can hardly accept
that it is possible that he could have seen them with the size of telescope he
used, however, due to his usually very precise measuring of positions and the
accuracy of his descriptions one would have great difficulty disputing that he did
in fact see them.
It is a delight for me to have his data available to consult as he almost always
used reference field stars to measure separation values that were applied in
establishing very good coordinates for the objects he observed, often measuring up
to as many as five different times over different years. Although like all
observers he occasionally took a stellar image to be nonstellar the investigator
using his data can almost always correctly determine just exactly what it was he
was referring to as a Nova and it must be understood that often for those objects
which we know now to be single or multiple stars and which he described as
appearing somewhat nebulous he generally mentioned in his descriptions that their
appearance was stellar and only suggestive of being nebular and that they should
be considered as being possibly dubious as to their nonstellar character.
As a matter of course I work out his coordinates for other field objects as his
coordinates are so good, using them as additional references for particularly
complex identity problems even when the actual object I may be investigating is
not one of Bigourdan's.
Bigourdan's 1919 publication, OBSERVATIONS DE NEBULEUSES ET D'AMAS STELLAIRES is I
believe one of the last published of the great visual surveys of nonstellar
objects and is in my opinion the best work ever produced in this field. His
micrometric measurements, usually from reference field stars in which he gives the
separation values to the objects he is examining down to one-hundreds of a second
of RA and tenths of an arcsecond declination, are of high accuracy. His selection
of reference stars is usually those of the BD catalogue, (Argelander 1863)
precessed to epoch 1900 and whenever Bigourdan was obliged to use anonymous stars
as reference he always measured and noted in his observations the separation
values between his anonymous reference stars and the nearest BD star, which is a
tremendous aid for the investigator.
As he generally made multiple observations of the objects he lists, often years
apart, his observations make for interesting reading and often he refers to other
field stars associated with the object he is describing, giving vital statistics
such as the separations and position angles involved, all of which can help
establish exactly the objects identity.
Bigourdan between the years 1887 and 1901 also published in the COMPTES RENDUS
four lists containing all of his discoveries that were to receive NGC and IC
identities and some of these were not included in his 1919 work.
These lists are almost certainly the sources for Dreyer's identities credited to
Bigourdan in the IC catalogues and are very important in that they serve as
confirmatory references for Bigourdan's "Missing Objects".
I am indebted to the great kindness of Brent Archinal for having copied and sent
to me these lists which are long out of print and therefore difficult to obtain.
M. JAVELLE :
M. Javelle was another excellent visual observer who observed with the 30 inch
refractor of the Nice Observatory in the south of France. With this size of
aperture he was able to find many of the fainter and smaller IC galaxies.
Due to the great kindness of Steven Gottlieb and Mr. P.D. Hingley, Librarian of
the Royal Astronomical Society, I was sent copies of Javelle's three catalogues in
which he lists all of his IC objects.
These catalogues are in two parts. Part I gives Javelle's Object number,
beginning with No.1 and ending with No. 1469 followed by the coordinates given for
the epoch 1860 and then a brief description of the each object. Part 2 repeats
the Javelle number, then gives the date and time of the observation followed by
the separation values given to one-hundreds of a second of RA and tenths of an
arcsecond Dec. from the reference star employed. Next comes the listing of the DM
reference star giving also its Mv. and then the star's coordinates again based
upon the epoch 1860.
It is perhaps of passing interest to note that not only did Javelle select the
same epoch (1860), as Dreyer had for his catalogues but Javelle also gave the
declination by North Polar Distance, thus providing continuity with the NGC.
Javelle's micrometric positions are usually excellent so that once the reference
stars have been located on the Palomar print it becomes very easy to find
Javelle's objects using his separations, however, I have found on occasion what
appear to be typographical errors in his positional data which have obviously
misled later authors of catalogues and papers. Some of these positional errors
are quite large while others appear to be caused by the insertion of the wrong
directional sign (+ or - ), as usually in such cases the amount of the separation
involved is correct. The investigator must always remember that with Javelle's
data one is working with North Polar Distance and not the now more commonly used
north and south declinations, therefore it is always necessary to reverse the NPD
precession signs for northern hemisphere objects.
MAX WOLF :
Although Professor Max Wolf is credited with a few discoveries in the IC I
catalogue it is his contribution to the IC II that makes up the vast majority of
galaxies credited to him. It was now that the examination of photographic plates
provided astronomers with some idea of the large number of nonstellar objects
existing in the sky and Wolf's studies of the plates taken with the 16 inch Bruce
refractor of the Heidelberg Observatory resulted in his publishing a number of
lists which were later used by Dreyer in his IC II.
Wolf divided his lists into specific zones, usually covering areas with high
concentrations of galaxies such as the Coma-Virgo regions where clustering of
galaxies occur.
His lists periodically include positional data and descriptions of NGC galaxies
and these can often be used as additional reference objects for locating some of
his associated discoveries by offset measurements using only the separation values
derived from only his data. Oddly enough although Wolf's coordinates are based
upon epoch 1875 he also employed the North Polar Declination in his lists.
Wolf's data often includes position angles for extended systems and his
descriptions are given in the letter style adopted by Dreyer in the NGC. One
rather nice feature is that for each of his objects Wolf gives the annual rate of
precession, a great help to the investigator who has to continually compute the
differences in RA and Declination to whatever epoch he happens to select to work
in for his investigations.
As would be expected Wolf's coordinates, given to either tenths or one hundreds of
a second RA and to either complete arcseconds or tenths of an arcsecond Dec.
depending on which list one is using, are of high accuracy, however, due to early
photographic problems and the fact that many of Wolf's objects have very compact
images it becomes at times extremely difficult to decide just exactly whether many
might be galaxies or instead are only stars which I am inclined to believe many of
them are. I should add that with the latest Second Generation versions of the
Digitized Sky Survey now available the ability to be able to distinguish many
nonstellar images from stellar ones has become much easier.
SCHWASSMANN :
This astronomer is credited with the discovery of IC galaxies which make up Wolf's
second list and which consists of discoveries made with a 6 inch lens.
Schwassmann's examination of these plates produced a significant number of new
galaxies, however, it would seem that he was more interested in recording all the
nebular images he found rather than trying to ascertain what their identities
might be, as in addition to mistaking stars for compact galaxies (nebulae), he
also on a number of occasions recorded images of known NGC objects without
indicating whether he was even aware of this.
One thing I have found out while employing his data is that his coordinates are
extremely good, enabling one to establish exactly just what images he recorded,
except of course when I did not find any image at the position he gave and had to
describe the identity as "Not Found".
Schwassmann's Coordinates are given for epoch 1900 and his descriptions are
similar to those found in Dreyer's catalogues with some additional combinations of
letters used for specific features.
There is no doubt that a considerable number of Schwassmann's objects are not
nebular, being either single or multiple stars, but obviously with the rather long
exposure time of the plates he examined some smudging or other image distortion is
understandable and this most likely accounts for the majority of his errors.
ROYAL FROST :
A large number of the discoveries credited to Frost are for objects located south
of declination - 28, photographed with the Harvard Observatory Bruce 24 inch
refractor located at their station in Arequipa, Peru. Even though in some cases I
was unable to verify the existence of some of his objects I would say that for the
most part Frost was describing actual nebular images. I would also have to say
that my only reservations with his data is that his coordinate values are given
only to tenths of a minute RA and his declination values to only the nearest
arcminute which naturally does not allow for precise pinpointing of any problem
identities involved in groups or clusters of associated galaxies. Frost's
coordinates are based upon epoch 1900 and his descriptions are mainly in complete
word form, using word abbreviations occasionally.
Part of the region examined by Frost coincides with that covered earlier by
Schwassmann and the Harvard list records some 200 additional objects and Frost
points out that 57 objects in the Schwassmann list do not appear on plates taken
at Arequipa, adding that 12 of these are actually either NGC galaxies or parts of
NGC galaxies and therefore were deliberately omitted from the Harvard list. He
also states that 36 objects listed by Schwassmann appear distinctly stellar on the
plates taken at the Harvard station in South America.
DELISLE STEWART.
Stewart was a colleague of Frost and continued and expanded the Harvard
Observatory's photographic survey of the Southern skies.
As with Frost the RA coordinates are given only to tenths of a minute of time and
the declinations only to whole minutes.
Stewart's contributions were the result of observations made between October 1898
and June 1901 and are presented in a paper in the Annals of the Harvard
Observatory vol lx, pp.151-172, titled Nebulae Discovered by Delisle Stewart.
As with Frost, it can be said that in the majority of cases the Novae he reports
do exist.
In order to assess the positional accuracy of the Harvard survey it is of interest
to know how they measured their coordinates from the plates they examined as it
indicates that beyond typographical errors their overlays should, if correctly
read, provide fairly accurate coordinates within the parameters they employed.
Separate plates were exposed at the different survey declinations with the
telescope on the meridian and the drive turned off in order to allow the stars to
form trails across the plates. The shutter was closed at one minute intervals,
breaking the trails, thus indicating the minutes in RA. Then these plates were
fastened with the film up on a table and a marker was pivoted from one end to
swing horizontally over the plates.
Adjustments were made until a fine point pencil could follow the middle of the
trails accurately. Celluloid film was then placed over the plates and the
corresponding curves of declination were traced on them. Intermediate curves were
then drawn at each 2 arcmin of declination, also the lines corresponding to each
minute of RA.
For the determining of the positions of the nonstellar objects on each plate the
brightest stars on each plate were arranged to closely conform to their 1900
positions and the film fastened on the edges so as to avoid misplacing. Finally
all NGC objects were reduced to 1900 epoch and identified on the plates after
which the non NGC objects visible were read off and listed as Survey discoveries.
During my investigations I came across a number of the Harvard objects that I
decided were "Not found" as at or close to the given coordinates no suitable
nonstellar images were found. Some of these identities have been assigned by one
or more of the modern authorities to galaxies found at distances from the original
coordinates that I consider to be beyond the general error level found to exist
for the Harvard Survey. As the majority of the Harvard objects can be confirmed
due in great part to their small level of positional offset from the more precise
modern coordinates I am particularly against accepting suggested candidates whose
coordinates differ to relatively large amounts in both RA and declination as I am
willing to concede that measuring errors of such amounts might be possible in one
coordinate but most unlikely for both, especially when the same exact plates have
other confirmed Harvard objects which compare very favorably with the modern
positions. It is my understanding that the original plates are still stored in
the Harvard Observatory's archives and hopefully at some future date they can be
examined in order to establish clearly the existence or non-existence of such
identities.
Finally, it is necessary to comment upon the accuracy of the coordinates furnished
by the observers at the Leander McCormick Observatory in their published papers,
(The Astronomical Journals No. 146 and No. 152), in which they give their data for
newly discovered Nebulae and which later received NGC identities.
Dreyer on page 10 of the NGC refers to the poor quality of this data and expresses
a hope that future lists from this source will be more accurate, which I am
delighted to say had good effect as their positions for their IC discoveries are
considerably better.
Their coordinates for their NGC discoveries are so bad , particularly in RA, that
it resulted in greatly misleading later IC discoverers, notably Javelle, who
finding objects and accurately measuring their positions, quite rightly considered
that these objects were novae and only through the efforts of Dr. Harold Corwin
who searched for the Leander McCormick objects with the aid of field sketches
made during the original observations, have we lately found that a number of these
are equivalent to IC identities.
THE MODERN SOURCES.
After I had completed examining the Palomar prints it became time to select which
modern sources I would examine and compare with the findings and conclusions I had
arrived at in order to ascertain whether such sources contained either errors of
identities or omissions of correct identities, such as listing existing IC
galaxies without credit . Following is a list of the selection I chose and some
information pertaining to these publications.
CATALOGUE OF GALAXIES AND CLUSTERS OF GALAXIES. (CGCG).
This six volume work compiled by F.Zwicky and colleagues at the California
Institute of Technology (1961 -68) is based upon examination of the Palomar
Observatory Photographic Sky Survey (1954).
In addition to listing a large number of galaxy clusters it also lists some 31,500
individual galaxies giving their NGC, IC or "Zwicky Number" which is obtained by
using the particular field number involved (each field corresponds to a single
Palomar print) followed by the numerical sequence determined by the objects order
of right ascension on the specific Palomar print.
The CGCG has a limiting magnitude of 15.5 Mp and does not list many of the IC
galaxies, however, as with all similar catalogues it does contain errors, some of
which concern identities in this part of my survey, and these errors will be
discussed in the LIST OF RESULTS.
The CGCG gives positions, for epoch 1950, but only to tenths of minutes in RA and
the nearest arcminute in Dec; however, generally I have seldom experienced
difficulty when using its coordinates in locating on the Palomar prints any of the
galaxies it lists and it appears to be a work in which there is no doubt that its
compilers did examine and measure the positions on the Palomar prints for every
galaxy they list, something not always evident with some of the catalogues
published later.
UPPSALA GENERAL CATALOGUE OF GALAXIES. (UGC).
This is an excellent single volume catalogue authored by P. Nilson of the Uppsala
Observatory in Sweden (1973), which lists some 12,921 galaxies north of
declination -2 degrees 30 arcmin and its coordinates, based upon epoch 1950 and Mp
data are taken directly from that of the CGCG.
Some additional features unique to this work are its inclusion of MCG identities
as well as the catalogues own numerical identities and of course the prime
identities which are those associated with the NGC and IC catalogues, also listed
are galaxy diameters measured from both blue and red Palomar prints, position
angles of an objects major axis, radial velocities both as referred to the sun and
corrected for solar motion and finally a "Notes" section which provides a wealth
of information related to the listed object, especially information which pertains
to closely associated galaxies.
I would have absolutely no hesitation in recommending this catalogue to any
serious observer and those possessing a copy of this now out of print work may
consider themselves fortunate.
MORPHOLOGICAL CATALOGUE OF GALAXIES. (MCG).
This Russian catalogue (VOLS I through IV) whose main authors are B.A. Vorontsov-
Velyaminov and V.P.Arhipova (1962 - 68) lists about 29,000 galaxies located north
of declination -33 degrees. Each galaxy has a MCG numerical identity and also
when applicable its NGC or IC identity.
Coordinates are based upon epoch 1950 and additional information given includes
Mp, image size in tenths of arcminutes and descriptions based upon a symbolic code
which is described and translated into English in the Introduction of Part I of
the catalogue. I also am fortunate in having a much more extensive private
translation in my personal collection.
In addition to having some identity errors or omissions there are often
considerable differences in coordinate values between this catalogue and other
modern sources.
A MASTER LIST OF NONSTELLAR OPTICAL ASTRONOMICAL OBJECTS. (MOL).
This is an extensive catalogue compiled by R.S. Dixon and G. Sonneborn and
published by the Ohio State University Press. It lists approximately 185,000
identities taken from 270 catalogues.
As with the NGC 2000 all IC identities are given and again when the authors were
aware of corrections to the original data they have included these corrections in
their catalogue, however, as a considerable number of IC galaxies have not been
previously checked as to type this catalogue has numerous IC identities listed as
"Nonstellar Objects" on the assumption that they all exist as such, even though I
feel certain that Dixon and Sonneborn are as equally well aware that many of these
might turn out to be otherwise.
The MOL gives its coordinates to the year 1950 and they are almost all precessed
directly from Dreyer's 1860 positions as is much of the identity data, therefore a
portion of the errors detected in the MOL result from errors present in the
original IC catalogues.
The coordinates are generally given to seconds of RA (occasionally to hundreds of
a second) and to minutes of arc declination (occasionally to arcsecs or tenths of
arcsecs.) I particularly liked this catalogue because it includes entries taken
from so many seldom consulted modern sources, allowing me to cross check identities
from these lists which often have references to very compact images whose Palomar
print appearance was extremely difficult to define as to type.
THIRD REFERENCE CATALOGUE OF BRIGHT GALAXIES. (RC3).
This is a revised and enlarged version of the previously published RC1 and RC2 by
G.and A. de Vaucouleurs et al.
The version I have is the electronic one and I am indebted to Dr. H G.Corwin (who
is one of the major contributors to this catalogue) for having very kindly sent me
a copy.
The RC3 data is contained in 10 columns detailing a wealth of information for each
of its entries. Of particular interest to me for my survey were:
Column 1, (Positions).
These are given for both equinox 2000 and equinox 1950.
The RA and Dec. given to 0.1 seconds of time and 1 arcsec when available, and to
0.1 minute of time and 1 arcmin otherwise.
Column 2. (Names).
NGC and IC designations and other identities such as Zwicky
number (CGCG), Nilson number (UGC), Vorontsov-Velyaminov number (MCG) and
Principal Galaxy Catalogue number (PGC) and
Column 3. (Types and Luminosity Classes).
The electronic version is constantly being updated by Corwin as corrections to
data becomes available, thus this catalogue, certainly in its computer version,
has to be considered as potentially one of the most accurate of its type for
future references.
THE DEEP SKY FIELD GUIDE (DSFG).
A handsomely produced catalogue compiled by M. Cragin, J. Lucyk and B. Rappaport.
It was originally conceived as an aid for those using the sky charts of the
Uranometria 2000.0, however, the amount of data it presents goes far beyond such a
limited use and should encourage amateurs to expand their observing programmes.
As would be expected, this catalogue is formatted by the chart numbers employed
for the individual maps as found in the Uranometria 2000.0. It lists coordinates,
objects name, visual magnitude, objects diameter, surface brightness, type,
position angle of major axis and an excellent Notes section with information
concerning field associated objects which should be of interest to all observers
and identity investigators.
The compilers of this work have produced a catalogue that obviously required a
great amount of researching in the modern professional catalogues, especially the
CGCG, UGC and MCG, therefore any identity errors it may contain can usually be
traced back to this three sources.
I am certainly aware that at least one of its contributors, M. Cragin, is
particularly interested in corrections to modern catalogues as I have had the
pleasure of conducting a valued correspondence with him on such matters and his
input and encouragement for my own investigative work is greatly appreciated by
me.
SOME CORRECTIONS TO DREYER'S CATALOGUES OF NEBULAE AND CLUSTERS. (CARLSON).
This is a famous paper by Dorothy Carlson published in 1940 in CONTRIBUTIONS FROM
THE MOUNT WILSON OBSERVATORY. ASTROPHYS. J. 91: 350 in which she presents the
results of her study of errors pertaining to the NGC and IC catalogues. The
majority of her conclusions are based upon her examination of photographic plates
made with both the 60 inch and 100 inch reflectors on Mount Wilson. Additionally
she includes corrections derived from other sources such as Dreyer, Reinmuth,
Helwan Observatory, Lick Observatory and certain Harvard Annals.
Although a majority of her corrections are valid some have been found to be
erroneous (certainly a warning to present and future investigators not to consider
that their own conclusions are infallible) and evidently some of her incorrect
conclusions stem from not having access to present day technology as it applies to
photographic film, as under her Table 1a heading "Objects to be stricken from the
New General Catalogue" and Table 1b "Objects to be stricken from the Index
Catalogues" she lists a number of "Not Found on Mt. Wilson plates," yet some of
these show as legitimate galaxy images on the Palomar Survey prints.
Another source of incorrect evaluation and something that has contributed to many
catalogue errors is equivalent identity. Often such identity is assigned by
catalogue compilers without having first consulted the observational data of the
person or persons involved in the original discoveries. Examination of such
original historical data often reveals that no equivalency was possible.
Carlson paper is an important contribution and has influenced the data found in
many of the catalogues which followed its publication.
THE PRINCIPAL GALAXIES CATALOGUE. (PGC).
This is the basis for the RC3 Catalogue compiled by G. Paturel and his colleagues
and contains data for 73197 galaxies located in both the northern and southern
hemispheres.
Among such information as cross checking with a majority of modern sources it
gives coordinates for both 1950 and 2000 epochs, morphological descriptions,
apparent major and minor axes, apparent magnitudes, radial velocities and position
angles.
The version I have employed is the electronic one provided by the ASTRONOMICAL
DATA CENTER. JAPAN on the Internet which is the complete catalogue, additionally I
am indebted to Dr. Clive Davenhall of the Royal Observatory, Edinburgh, Scotland,
who at my request kindly sent to me a specially formatted electronic version of
the PGC which listed only the data pertaining to the IC galaxies.
AN EXTRAGALACTIC DATA BASE. IV. ERRORS AND MISPRINTS IN CATALOGUES OF GALAXIES.
(PGC).
This also is a paper (ASTRONOMY & ASTROPHHYSICS, SUPPLEMENT SERIES 91, 371-397.
1991. G.PATUREL ET AL), dealing with discrepancies found by the authors in various
modern catalogues.
Although once again a majority of the corrections are valid some of them are
definitely incorrect (I refer only to those that concern identity problems and not
to any possible coordinate errors that might exist).
Table 1 of this paper is devoted to equivalency identities involving NGC and IC
galaxies. Table 2 contains errors in various catalogues including the CGCG, MCG
and UGC and I find myself to be in disagreement with a number of the conclusions
in both Tables.
THE ACCURATE POSITIONS LIST. (APL or NGCICPOS).
This is a set of coordinates for most of the NGC and IC identities as measured by
various quoted authorities and collected by Dr. Harold G. Corwin and posted on his
NGC/IC DATABASE FILES for the NGC PROJECT (WWW INTERNET). In addition to
positional data it includes corrections for many entries pertaining to
equivalency, incorrect identity and coordinate errors. Corwin has cautioned that
possibly some of the conclusions may be subject to further correction based upon
investigations currently being carried out. I wish to make it clear that the copy
I have consulted is dated Jan. 16th 2004 and that all of my references to the APL
are based upon the data as printed in this dated copy.
NGC/IC BUG LIST.
A collection by Dr. Harold G. Corwin of some of his findings and conclusions from
his many years investigations into erroneous information concerning NGC and IC
objects. As the leading authority on such matters and one who has been both an
inspiration and guide to me I am most grateful to him for his kindness and
support.
W. STEINICKE. NGC/IC DATABASE. (CORRECTED IC'S)
This is a complete DATABASE FILE of IC objects compiled and presented by Wolfgang
Steinicke on the WORLD WIDE WEB (INTERNET. Dated March 31st 2005) for the NGC/IC
PROJECT.
NED. NASA EXTRAGALACTIC DATABASE.
Contains a considerable amount of data and accessable tools for researching
Deep-Sky objects.
SET OF IDENTIFICATIONS. MEASUREMENTS, BIBLIOGRAPHY FOR ASTRONOMICAL DATA. (SIMBAD).
The European counterpart of NED. Contains a large amount of data on mostly
Nonstellar Objects.
REMARKS.
Having spent the better part of the past ten years examining and evaluating the
observational data contained in the historical lists of the various contributors
whose observations resulted in producing the IC galaxy identities presented as a
part of this study I would like to express my unbounded admiration for the
excellence of their work. Furthermore J.L.E.Dreyer, the compiler and author of
the IC catalogues, certainly deserves every bit of the esteem and credit
associated with his name as the par excellence in listing the historical deep sky
objects. No greater tribute can be paid to his memory than the fact that more
than 100 years after the publication of the NGC and IC I his identities are still
paramount in today's astronomy.
Finally it would definitely appear that in the field of seeking solutions to
identity problems there is sure to be some disagreement between investigators and
this can only be a healthy situation, as it is through debating such disagreements
and from examination of all the claims and deciding which arguments, until
replaced by more convincing data, are the most tenable that science has always
advanced.
It is in this spirit I offer the conclusions listed in this survey and also in the
hope that other amateurs will become interested in a part of astronomy that not
only combines the history of the science we love with our present day astronomical
interests but also provides a fascinating field of study with many surprises.
ACKNOWLEDGEMENTS.
In any work similar to this an author is usually dependent upon assistance and
certainly in my own case I have been afforded excellent help from a number of
colleagues, both through the provision of source material and in the rendering of
valued advice and opinions on some of the conclusions I have drawn.
Other assistance came in the form of interest in this project expressed in private
correspondence which has been of great encouragement to me. I especially wish to
thank fellow Webb Society member Steve Gottlieb who searched the archives for much
of the historical sources employed in this study and without which it would have
been impossible to have carried out such a survey. Steve, in addition to being an
excellent observer, is one of the present day leading investigators of identity
errors and he has been responsible for a large number of the corrections to errors
in the identities found to exist in the RNGC and other sources.
To Dr. Harold G. Corwin of the California Institute of Technology my thanks and
appreciation for not only sending me a copy of the computer version of the RC3 but
who always found the time to examine and comment on a number of the more complex
identity problems I encountered.
Dr. A. C. Davenhall, Royal Observatory, Scotland, for sending me a printout copy
of all the IC galaxy identities north of Declination - 28 degrees giving their
coordinates to both equinox 1950 and 2000. Additionally, I am indebted to Dr.
Davenhall for his kindness in taking the time to prepare and send to me an
electronic version of the PGC listing only its data pertaining to the IC galaxies
which greatly aided my research and vastly shortened the time required by me to
make comparison studies of the historical and modern data.
Peter D. Hingley, Librarian of the Royal Astronomical Society who most graciously
sent me a copy of Javelle's Third Catalogue and Steven J. Hynes, former editor of
the W.S.Q.J. for mailing to me Hickson's papers on galaxy groups and who also
provided me much appreciated support for my investigative studies over the years.
To Wolfgang Steinicke who kindly sent me a printed copy of his Revised New General
Catalogue and Index Catalogue. I have referred to it extensively in my
investigations.
My thanks also to Alister Ling and Paul Brown who have themselves made many
contributions to solving identity problems and have brought to my attention many
catalogue inconsistencies, also Murray Cragin who very kindly sent me a personal
copy of his The Deep-Sky Field Guide to Uranometria 2000.0 and is now becoming
involved in correcting identity errors. Also I wish to express my sincere thanks
to Brent A. Archinal, U.S. Naval Observatory, Washington D.C. who in addition to
providing me with important historical data, took the time to examine and send me
a detailed evaluation of an earlier version of this work. His analysis and
suggestions were of immense importance towards improving my presentation.
To M. Etienne Le Monnier of Brussels, Belgium, the grandson of M. Guillaume
Bigourdan, whom I have had the pleasure to become acquainted with through personal
correspondence initiated by Mme. Suzanne Débarbat of the Paris Observatory and who
has most kindly sent to me items of extreme importance dealing with his
grandfather's astronomical life in addition to a most appreciated photograph of M.
Bigourdan which presently adorns my work desk in my study at home.
To Dr. Luis Carrasco, former Director of the San Pedro de Martir Observatory, Baja
California, Mexico. also Dr. Alberto Lopez, staff astronomer of the Observatorio
Astronomico Nacional de Mexico and Maria Ellena, Librarian, for granting me access
to a large portion of the modern literature I consulted in the library of the
Instituto de Astronomia, Ensenada, Mexico., especially the complete set of the
Palomar Survey prints, my thanks and appreciation. Although this Institution is
entirely involved in professional astronomical research they extended to me, an
amateur, all of the many resources available to them in order to assist me in my
survey. Muchisimas Gracias.
Finally, I would like to express my admiration and sincere thanks to Bob Erdmann,
the Project's Webmaster, who in addition to his own contributions to the NGC/IC
Project in the form of his imaging and data information, has created a website
that presents in a most informative manner the aims and results of those involved
in constructing a cleaner version of the NGC and IC objects. The quality of his
work can be gauged by the views expressed in the many astronomical references that
have lauded the site as being one of excellence and without Bob's hard work we
other members of the group would have virtually little audience.
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