Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/~astro/aotms/performance/99-03.ps Äàòà èçìåíåíèÿ: Thu Apr 15 20:37:14 1999 Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 05:44:36 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: planetary nebula

Single­Epoch Measurements of Broadband
Radio Continuum Spectra
A Cast of Summer Students 1 Jo Ann Eder Tapasi Ghosh,
Chris Salter.
NAIC/AO, P. O. Box 995, Arecibo, Puerto Rico 00613.
April 13, 1999
Abstract
The ability of the upgraded Arecibo 305­m telescope to produce ``quasi­
instantaneous'' radio continuum spectra covering over a decade of frequency
has been investigated, the study being undertaken as an Arecibo Observatory 2
summer­student observing project. Within the limits of early post­upgrade in­
strumentation and telescope performance, it was found to be relatively easy for
inexperienced observers to obtain the measurements needed to achieve the above
objective. Good­quality spectra were produced for three quasars (J1609+266,
J2115+295 and J2203+317) which exhibited mutually different spectral shapes.
The planetary nebula, G064.7+05.0, was also included in the target list. This
is shown to be optically thick at 1.4 GHz, while only an upper limit to its flux
density could be determined at 430 MHz.
1 Introduction
Radio continuum spectra are usually ``synthesised'' from already available flux
density measurements made at many different epochs. Much more of a rarity are
spectra compiled from flux densities measured quasi­simultaneously at a number
of frequencies. However, such spectra have been obtained using the VLA (i.e.
for extragalactic radio supernovae, stellar variables, some AGNs, etc.), and by
University of Michigan (UMRAO) observers for a sample of extragalactic variable
1 Angel Alejandro Qui~nones (UPR­Humacao), Monique Aller (Wellesley), Yira Cordero Lebron
(UPR­Humacao), Ingrid Daubar (Cornell), Simon DeDeo (Harvard), David Kaplan (Cornell), Dale
Kocevski (U. of Michigan), Felix Mercado Cortes (U. Metropolitana), Benjamin D. Oppenheimer
(Harvard), Celia Salmeron (U. of Houston)
2 The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is
operated by Cornell Univ. under a cooperative agreement with the National Science Foundation.
1

sources between 5 and 15 GHz. The upgraded Arecibo telescope, with its ability
to switch between frequencies in a matter of seconds, would seem potentially well
suited to such work, providing both speed and ``photometric'' performance.
To investigate the present quality of such Arecibo measurements, and also to
serve as ``hands­on'' observing experience, the 1998 Arecibo summer students
made measurements of a number of continuum sources at four different frequen­
cies spanning over a decade in frequency on two nights in July 1998. Sources
of differing spectral types were chosen as targets, while two steep­spectrum
(ff ? 0:5; S/ š \Gammaff ) objects of moderate strength served as flux­density cali­
brators. The summer students were split into two groups of five, with no overlap
between the members present on each of the nights. The observations were over­
seen by Jo Ann Eder and Chris Salter. The students themselves reduced much
of the data, their measured values being checked and refined by Chris Salter and
Tapasi Ghosh, who also planned the measurements.
2 The Sample
Pending realignment work scheduled for late 1998, the Arecibo telescope is known
to have greater, less symmetric, gain variations with azimuth and zenith angle
than specified in its upgrade design goals. Hence, we selected sources within a
relatively small declination range (29 ffi ! Dec ! 33 ffi ), separated in Right Ascen­
sion by about an hour each. This was to permit observing within a rather limited
range of azimuth and zenith angle, without too much detailed scheduling being
demanded of the student observers.
The selected steep­spectrum calibrator sources, J1831+291 and J0040+331, have
spectral indices of about 0.6 and 0.8 respectively (K¨uhr et al. 1981). In the NVSS
survey made with the VLA in its D­array configuration (Condon et al. 1998),
both are listed as being smaller than 15 arcsec, meaning that they are essentially
point sources to Arecibo, even at the highest frequency presently available of 5
GHz.
The ``target'' sources were as follows;
ffl Two flat, or inverted, spectrum quasars, J2115+295 and J2203+317, where
the first source is a few times weaker than the latter.
ffl The planetary nebula, G064.7+05.0 (J1934+305). This source was selected
from the catalog of planetary nebulae from NVSS (Condon & Kaplan 1998).
Together, Condon & Kaplan and the full NVSS catalog show the source to
be smaller than 15 arcsec, relatively unconfused, and of about 0.25­Jy flux
density at L­band.
ffl On the first observing night, the observations began sufficiently early that
a test source, J1609+266, was used to check out the observing procedures
2

Table 1: Target Sources
Source RA Dec S(1.4 GHz) Other Name
(J2000) (J2000) (mJy)
Planetary Neb
G064.7+05.0 19 34 45.2 30 30 59 245
AGNs
J1609+266 16 09 13.3 26 41 29 4775 CTD93
J2115+295 21 15 29.4 29 33 38 975
J2203+317 22 03 15.0 31 45 38 2879 4C31.63
Calibrator
J1831+291 18 31 14.9 29 07 10 2924 4C29.56
J0040+331 00 40 55.1 33 10 08 3224 3C19
at 430, 1405 and 2380 MHz before moving on to the first program source
(J1831+291). J1609+266 is a GHz­peaked spectrum quasar which shows
``compact­double'' structure in VLBI images (though see Shaffer & Keller­
mann 1998). As these test measurements were recorded in the data file,
they too were reduced as per the other targets, despite the declination of
J1609+266 being outside the 29 ffi -- 33 ffi range.
A full source list is presented in Table 1.
3 The Observations
The observations were made on the nights of July 9 -- 10 and 14 -- 15, 1998. A
late start on July 14 -- 15, plus finding that from an earlier S­band radar run the
protective cover had been left over the –6­cm horn, necessitating a trip to the
feed turret, meant that the calibrator source, J1831+291, was only observed at
1405 MHz on that occasion.
The students cabled up the square­law detectors, the oscilloscope display and
the radar interface (continuum data logger) as per instructions (Perillat, private
communication). They also checked that the recorded values were relative to
a true zero level. At L­Band, the ``L­Narrow'' receiver was used. All receivers
responded to circular polarization, except the C­band receiver which was set up
for linear polarization. Data­taking with the radar interface was initiated, and
the observations on each source were cycled through L­band, C­band, 430 MHz
and S­band in that order. The students made the final scheduling of the sources
such as to minimize the range of azimuth and zenith angle involved (see Section
2 above). Once the telescope was pointed to a given target, the operations
performed at each frequency were;
3

1. the feed turret was positioned for the appropriate receiver.
2. The correct IF/LO configuration was set up. The chosen center frequencies
in observing sequence were 1405, 5000, 430 and 2380 MHz. A pair of 5­
MHz I.F. filters centered at 260 MHz were used for all frequencies except
C­band, where a pair of ``quasi­50 MHz'' filters were employed. This use of
wider bandwidth at C­band was useful given the lower telescope efficiency
there pending upcoming dome alignment work.
3. The I.F. attenuators were adjusted to give an appropriate signal level into
the radar interface to avoid saturation.
4. A pair of orthogonal 2­minute cross scans were made in ``great­circle'' co­
ordinates, first in ``cross zenith angle'', then in zenith angle (using the tele­
scope drive procedure ``crossgc''). The lengths of the arms of the crosses
were 20, 6, 60 and 12 arcmin respectively for the frequency order given
above. These represent about 5--6 \Theta HPBW at each frequency.
5. After the cross scans were completed, the telescope was stopped. When
the pointing had moved off the source, the noise source was fired for 30 sec.
The injection of these steps of time­invariant signal power permitted highly
accurate intercalibration of the different measurements at each frequency.
6. In real time, the students monitored all stages of the observations from the
Observing Room using the Analyz reduction package.
7. Full notes were taken, this task being rotated between the individual stu­
dents.
The complete data taking was run by the students, each taking their turn to act
as team coordinator for the above operations.
A number of instrumental problems were encountered during the runs. All were
subsequently fixed by the electronics division. On the night of July 9 -- 10, the
polarization­B channel of the S­Band system dropped out intermittently, and
data for J1831+291 and G064.7+05.0 were only acquired with a single circular
polarization. On the night of July 14 -- 15, only the polarization­A channel of the
C­Band receiver received the noise diode signal; calibration for the other channel
was made assuming a constant value of T sys (see below). At 430 MHz, only a
single receiver channel was available on both nights.
4 Data Reduction
Data reduction was made using the Analyz analysis package. For each cross scan,
the data was baselined by subtracting a straight line fitted to selected minima
on either side of the transit. A Gaussian was then fitted to the central section of
4

Table 2: Azimuth and Zenith Angle Ranges
Freq (MHz) \DeltaAz (Jul 9) \DeltaZA (Jul 9) \DeltaAz (Jul 14) \DeltaZA (Jul 14)
430 163 ffi -- 201 ffi 11.6 ffi -- 14.8 ffi 143 ffi -- 167 ffi 14.4 ffi -- 17.2 ffi
1405 192 ffi -- 225 ffi 13.7 ffi -- 16.6 ffi 156 ffi -- 190 ffi 11.3 ffi -- 15.1 ffi
2380 151 ffi -- 173 ffi 11.0 ffi -- 15.6 ffi 132 ffi -- 158 ffi 16.2 ffi -- 19.2 ffi
5000 181 ffi -- 217 ffi 12.7 ffi -- 15.3 ffi 149 ffi -- 177 ffi 12.7 ffi -- 16.0 ffi
the main beam response. Next, after baselining the appropriate data section, the
mean and rms of the calibration deflection was computed. During the analysis,
the following information was tabulated;
1. Azimuth and elevation of scan.
2. The off­source intensity due to the total ``system temperature''.
3. The fitted Gaussian height.
4. The time of transit (yielding the pointing offset).
5. The HPBW.
6. the noise­source intensity.
The spread of azimuth and zenith angle for the calibrators and main targets, i.e.
excluding J1609+266, are given in Table 2.
A number of parameters related to system performance are detailed in Tables 3
-- 6. The mean HPBW's on the two observing days are given in Cols. 2 and 3
of Table 3. Col. 4 contains the ratio of the main beam area (1.133 HPBWAZ \Theta
HPBWZA ) at 1405 MHz to that at the other frequencies as normalized by the
square of the ratio of frequencies. The early post­upgrade deterioration in per­
formance with increasing frequency is clearly seen at the two higher frequencies.
This is also illustrated by the maximum observed sidelobe level as exemplified
by observations of J0040+331 on July 10 (Col. 5). As the frequency increases,
the principal sidelobe increasingly has the form of a ``coma lobe''.
The mean pointing offsets, and the rms pointing about these, at the different
frequencies are given in Table 4. Although the range of azimuth/zenith angle
covered was rather small, the pointing at L­band and above was found to be
excellent. The values at 430 MHz reflect the situation that little pointing effort
has yet been expended at this frequency.
The System Equivalent Flux Densities (SEFDs) adjacent to the calibrator sources
are tabulated in Table 5. The flux densities used for J1831+291 and J0040+331
were computed from the formulae given for these sources by K¨uhr et al. (1981),
5

Table 3: Telescope Beam Parameters
Freq HPBW (Jul 9) HPBW (Jul 14) Beam Area Max. sidelobe
(MHz) (AZ \Theta ZA) (AZ \Theta ZA) (Normalized) (dB)
430 650 00 \Theta 732 00 624 00 \Theta 741 00 1.029 13.2 (ZA=14.9)
1405 202 00 \Theta 227 00 199 00 \Theta 224 00 -- 12.4 (ZA=16.8)
2380 125 00 \Theta 144 00 124 00 \Theta 148 00 0.865 10.9 (ZA=14.9)
5000 63.7 00 \Theta 76.5 00 63.0 00 \Theta 72.3 00 0.758 9.2 (ZA=15.4)
Table 4: Pointing Parameters for each Frequency
Freq (MHz) Az Offset \DeltaAz rms ZA Offset \DeltaZA rms
430 +96.1 00 11.8 00 +7.6 00 22.0 00
1405 +5.5 00 4.1 00 +0.6 00 2.6 00
2380 +3.1 00 6.2 00 +0.0 00 2.2 00
5000 --4.6 00 5.7 00 --1.2 00 3.6 00
and are on the scale of Baars et al. (1977). It should be remembered that at
430 MHz, J1831+291 and J0040+331 are seen against celestial backgrounds of
T b ú 34:5 and 22 K respectively, these values being extrapolated from the 408­
MHz survey of Haslam et al. (1982). This is expected to add about 3.8 and
2.4 Jy to the respective SEFDs. We also note that the 430­MHz receiver was
uncooled on July 14 -- 15, (and swapped to the other polarization channel!)
In Table 6, Cols. 3 and 5, we present the mean value of T sys in units of the
noise source intensity, with the rms's of all individual measured values in Cols. 4
and 6. The T sys values at 430 MHz correlate well with the celestial background
temperatures (Fig. 1), explaining the much higher rms's at this frequency. It is
of interest that the best­fit straight line to Fig. 1 gives an extrapolated T sys of
44 K for zero sky brightness. This yields a 430­MHz point­source response for
the telescope of ú9.0 K/Jy, close the value expected at this frequency.
5 Results
The directly measured Gaussian fits for the sources had their peak deflections
corrected for the pointing errors estimated from the orthogonal scan of each pair.
Next, they were normalized by the noise­source deflections, and then converted
into Jy using the flux densities for the two calibrators from K¨uhr et al. (1981).
The derived flux densities for the target sources are given in Table 7. In this table,
the 1405­MHz flux densities are the average of both observing days, while only
the results from July 9 -- 10 are given for the other frequencies, these representing
6

Table 5: System Equivalent Flux Density at each Frequency
Freq Date Source Az El T sys (Ch A) T sys (Ch B)
(MHz) (deg) (deg) (Jy) (Jy)
430 Jul 9 J1831+291 201 11.7 -- 8.77
Jul 9 J0040+331 183 14.8 -- 7.78
Jul 14 J0040+331 167 15.2 10.49 --
1405 Jul 9 J1831+291 227 15.5 3.97 3.65
Jul 9 J0040+331 206 16.6 4.19 3.82
Jul 14 J1831+291 156 12.0 3.84 3.49
Jul 14 J0040+331 190 15.1 4.10 3.74
2380 Jul 9 J1831+291 170 11.0 4.19 ­
Jul 9 J0040+331 173 15.0 4.59 4.13
Jul 14 J0040+331 156 16.5 4.84 4.12
5000 Jul 9 J1831+291 217 13.9 10.62 10.95
Jul 9 J0040+331 194 15.3 14.54 14.66
Jul 14 J0040+331 177 14.8 17.78 16.87
Table 6: T sys /T cal
Freq Date T sys /T cal RMS T sys /T cal RMS
(MHz) (1998) (Ch A) (Ch B)
430 Jul 9 -- -- 1.44 0.16 (10.9%)
Jul 14 1.81 0.14 (7.6%) -- --
1405 Jul 9 18.60 0.30 (1.6%) 16.19 0.22 (1.4%)
Jul 14 18.13 0.36 (2.0%) 15.65 0.46 (2.9%)
2380 Jul 9 4.17 0.02 (0.4%) 3.64 0.04 (1.2%)
Jul 14 4.42 0.04 (0.9%) 3.66 0.05 (1.3%)
5000 Jul 9 2.88 0.02 (0.6%) 4.74 0.02 (0.5%)
Jul 14 2.90 0.03 (1.0%) -- --
7

Figure 1: The measured 430­MHz signal versus the celestial brightness temperature,
TB , at that frequency as derived from Haslam et al. (1982).
Table 7: Flux Densities of Target Sources
Source Freq Flux Density Error
(MHz) (Jy) (Jy)
J1609+266 430 3.379 0.132
1405 5.063 0.125
2380 3.502 0.147
5000 -- --
G064.7+05.0 430 !0.038 --
1405 0.265 0.008
2380 0.475 0.023
5000 0.587 0.071
J2115+295 430 0.464 0.026
1405 0.792 0.021
2380 0.904 0.040
5000 1.118 0.136
J2203+317 430 3.216 0.132
1405 2.597 0.064
2380 2.441 0.102
5000 2.436 0.300
8

Table 8: Derived Flux­Density Differences for the Two Epochs
Source Freq \DeltaS \DeltaS ZA
(MHz) (Jy) (%) (deg)
J2115+295 430 --0.002 --0.4 11.7/14.4
1405 --0.017 --2.1 16.3/11.3
2380 --0.070 --7.7 11.7/16.7
5000 0.144 12.9 14.3/12.7
J2203+317 430 --0.347 --10.8 14.1/17.3
1405 --0.018 --0.69 13.7/14.5
2380 --0.285 --11.7 15.6/18.7
5000 0.650 26.7 13.4/16.0
G064.7+05.0 430 -- -- --
1405 --0.012 --4.7 15.1/13.2
2380 --0.100 --21.1 12.5/19.3
5000 0.137 23.3 12.7/14.6
J0040+331 430 -- -- 14.8/15.2
1405 -- -- 16.6/15.1
2380 -- -- 15.0/16.4
5000 -- -- 15.3/14.9
the data for which observations of both calibrators were available. The errors
given in Col. 4 of the table are the quadratic sum of the error derived from
the disagreement between calibration factors derived independently from the
two calibrators, and the internal spread of the values derived from individual
measurements. No error is included for the likely deviation of the adopted flux
densities of the calibrators from their true Baars et al. (1977) values. This is
believed to be about 5% for each calibrator.
To permit meaningful inter­comparison, the measurements on July 9--10 and 14--
15, 1998 were both reduced using only the source J0040+331 as calibrator, this
being common to all frequencies on both days. The difference between the derived
flux densities on the two days are listed in Table 8. It should be remembered
that while the sources were observed within a relatively small range of azimuth
and zenith angle, no correction was applied for the residual azimuth/zenith­angle
differences. In particular, the telescope gain at (and presumably below) 1.4 GHz
is known to be relatively constant for ZA ! ¸15 ffi , but to decrease monotonically
beyond this. An example of this is the ú --10% difference in the flux densities
for J2203+317 derived at 430 MHz for the two epochs. If we correct the gain for
the high zenith angle of the source relative to the calibrator on the second epoch
using more recent 430­MHz observations, this difference is completely accounted
for. In fact, taking this into account, the values between the two epochs at 430
and 1405 MHz agree to better than 5% for all sources.
9

Figure 2: The 4.8­GHz variability of J2203+317 over the past 17 yr, derived from the
UMRAO database monthly averages.
Figure 3: The 4.8­GHz variability of J1609+266 between 1983 and 1986, derived from
the UMRAO database monthly averages.
10

Telescope commissioning observations have established that the system gain be­
comes an increasingly complicated function of both azimuth and zenith angle as
the frequency increases. This is also demonstrated by the differences between
our two epochs at 2380 and 5000 MHz, which show a progressive increase in
magnitude with frequency, and are systematically negative and positive respec­
tively. This latter phenomenon is presumably due to systematic effects from
the J0040+331 observations. However, even at these higher frequencies, the
mean differences of 13% and 21% suggest that the uncertainties in the flux­
density values at these two frequencies in Table 7 due to this complex gain
behavior are 6.5% and 10.5% respectively, using the two calibrators observed
on the first epoch. These values are, in fact, consistent with the calibration
differences found for the two calibrator sources at the first epoch, and which
are included in the errors given in Table 7. Of course, we cannot a priori ex­
clude some contribution to the measured differences at the two epochs from
actual source variations. However, monthly 4.8­GHz averages from the UM­
RAO database (http://www.astro.lsa.umich.edu:80/obs/radiotel/radiotel.html;
Aller et al. 1985) for the quasar, 2203+317 (Fig 2) suggest that, while this source
has large long­term variations, these variations occur on the time scale of months
rather than days. Similarly, J1609+266 is found from the UMRAO monthly av­
erages between 1983 and 1986 (the period over which it was monitored) to be
essentially non­variable at 4.8 GHz (Fig. 3), and it is therefore unlikely to have
varied significantly over 5 days at our highest observed frequency of 2.38 GHz.
The UMRAO database contains only a few measurements of 2115+295 between
1982 and 1985. These are at 8.0 and 14.5 GHz, but suggest that the source is
not strongly variable on the time scale of a month.
6 Discussion
All the spectra derived from our measurements (the lower panes in Figs. 4 -- 7) are
seen to be smooth within the errors. This confirms the power of the telescope,
even in its early post­upgrade incarnation, to produce the quality broadband
single­epoch spectra which were the objective of the present project. We will
now briefly discuss the astronomical significance of the results obtained.
6.1 The Three Quasar Targets
The spectra derived from published data are shown in the upper panes of Figs. 4
-- 6. These suggest that while the GPS source, J1609+266 is not strongly variable
over the years covered by these measurements, the large spreads in the data for
the sources J2115+295 and J2203+317 indicate that these vary significantly on
the time scale of years. (For the latter source, this is clearly seen in the UMRAO
4.8­GHz measurements of Fig. 2.)
11

The new Arecibo flux densities provide quasi­snapshot spectra for these sources.
The GHz peak in the spectrum of J1609+266 is clearly defined by the three flux
densities in the lower pane of Fig. 4. For the two variable quasars, the spectral
``snapshots'' show smooth spectra over more than a decade of frequency. That of
J2115+295 (lower pane of Fig. 5) is the more interesting, showing a significantly
inverted spectrum, with a spectral index of ff 5000
1405 ú \Gamma0:30 above 1405 MHz, and
an apparent steepening to ff 1405
430 ú \Gamma0:45 below this. In contrast, J2203+317
displays a classic flat spectrum at the higher frequencies, with a mildly positive
spectral index below 1 GHz (lower pane of Fig. 6). In respect of these spectral
differences, it may be of significance that although both sources show structure
on the milliarcsec scale, recent images from VLBI observations made between 2.3
and 15 GHz (Fey & Charlot 1997; Kellermann et al. 1998) show J2115+295 to
be considerably the more compact of the two. This would suggest that optical­
depth effects may be more pronounced for this source, consistent with its inverted
spectrum. In fact, J2203+317 displays a very beautiful core­jet morphology at
2.3 GHz on the scale of a few tens of milliarcsec.
6.2 G064.7+05.0
The planetary nebula, G064.7+05.0, is found to be significantly optically thick
below 5 GHz (Fig. 7). From our measured flux densities, we derive an
optical depth of Ü ú 2:5 at 1.4 GHz for a pure brehmstrahlung spectrum.
The predicted flux density at 2.38 GHz then agrees very well with the mea­
sured value at that frequency in Table 7. The predicted flux density of
27 mJy at 430 MHz is consistent with the upper limit of 38 mJy given in Ta­
ble 7, as is the non­appearance of the source in the 327­MHz WENSS survey
(http://www.strw.LeidenUniv.nl/%7Edpf/wenss/). We note that the 430­MHz
upper limit was derived from the actual scans, but the value of 38 mJy is similar
to the predicted rms confusion for Arecibo at 430 MHz of 40 mJy obtained from
the formula of Condon (1987).
7 Conclusions
The present investigation was observed entirely by a group of undergraduate
summer students at Arecibo Observatory, many having their first observational
experience. The success of the project in demonstrating that quality ``quasi­
snapshot'' spectra covering over a decade of frequency can be made with the
rebuilt instrument, also demonstrates the ease with which relatively complicated
experiments can now be observed (as it does the quality of the students!) The
moderate gain changes with both azimuth and zenith angle present for mea­
surements at the higher frequencies during the summer of 1998 should soon be
reduced to the design values in ZA, and hopefully eliminated in respect of az­
imuth, following the adjustment of the Gregorian dome attitude in late 1998. As
12

only a small gain­ZA dependency should be present subsequently, with only a
relatively simple correction being needed to account for this, very high quality
spectral measurements should then be possible, eventually spanning a frequency
range from 300 MHz to 10 GHz.
In addition, a continuum correlation polarimeter is presently nearing completion
at Arecibo, and full Stokes­parameter information should soon be available at
no extra cost but data volume for all continuum observations. The possibility of
measurements across a 30:1 frequency range for studies of total­intensity spectra,
Faraday rotation and depolarization is highly exciting.
Acknowledgements
The summer students are grateful for support from the NSF Research Experi­
ence for Undergraduates Program, the Univ. Metropolitana, and the Univ. of
Houston. We wish to thank Phil Perillat without whom the project would not
have been possible. We are very grateful to the Arecibo telescope operators who
cheerfully helped guide us through the observing sessions.
References
Aller, H. D., Aller, M. F., Latimer, G. E. and Hodge, P. E. 1985 Astrophys. J. Suppl. 59, 513.
Baars, J. W. M., Genzel, R., Pauliny­Toth, I. I. K. and Witzel, A. 1977 Astron.
& Astrophys. 61, 99.
Condon, J. J. 1987 ``Scientific Benefits of an Upgraded Arecibo Telescope'', Eds.
Taylor, J. H. and Davis, M. M., NAIC, P89.
Condon, J. J., Cotton, W. D., Greisen, E. W., Yin, Q. F., Perley, R. A., Taylor,
G. B. and Broderick, J. J. 1998 Astron. J. 115, 1693.
Condon, J. J. and Kaplan, D. L. 1998 Astrophys. J. Suppl. Ser. 117, 361.
Fey, A. L. and Charlot, P. 1997 Astrophys. J. Suppl. Ser. 111, 95.
Haslam, C. G. T., Salter, C. J., Stoffel, H. and Wilson, W. E. 1982 Astron. &
Astrophys. Suppl. Ser. 47, 1.
Kellermann, K. I., Vermeulen, R. C., Zensus, J. A. and Cohen, M. H. 1998 Astron.
J. 115, 1295.
K¨uhr, H., Witzel, A., Pauliny­Toth, I. I. K. and Nauber, U. 1981 Astron. Astro­
phys. Suppl. 45, 367.
Shaffer, D. B. and Kellermann, K. I. 1998 IAU Colloquium No. 164, Eds. Zensus,
J. A., Taylor, G. B. and Wrobel, J. M., A.S.P. Conf. Ser. No. 144, P191.
13

Figure 4: Continuum spectra for J1609+266 (CTD93) between 300 MHz and 10
GHz, a) for data taken from K¨uhr et al. (1981), the NVSS Survey (1998), White
& Becker (1992), the GB6 Catalog, the UMRAO database and the Texas Catalog
(http://utrao.as.utexas.edu/txs.html) and, b) for the new Arecibo data contained in
Table 7.
14

Figure 5: Continuum spectra for J2115+295 between 300 MHz and 10 GHz, a) for
data taken from K¨uhr et al. (1981), the NVSS Survey (1998), the WENSS Survey
(1998), White & Becker (1992), the GB6 Catalog, the UMRAO database and the
Texas Catalog (http://utrao.as.utexas.edu/txs.html) and, b) for the new Arecibo data
contained in Table 7.
15

Figure 6: Continuum spectra for J2203+317 between 300 MHz and 10 GHz, a)
for data taken from K¨uhr et al. (1981), the NVSS Survey (1998), the WENSS
Survey (1998), White & Becker (1992), the GB6 Catalog and the Texas Catalog
(http://utrao.as.utexas.edu/txs.html) and, b) for the new Arecibo data contained in
Table 7.
16

Figure 7: Continuum spectra for Planetary Nebula G064.7+05.0 between 300 MHz
and 10 GHz, a) for data taken from the Einline database, the NVSS Survey (1998),
the WENSS Survey (1998), White & Becker (1992), and the GB6 Catalog and, b) for
the new Arecibo data contained in Table 7. The values plotted as crosses from the
WENSS survey at 327 MHz (top figure), and Arecibo at 430 MHz (bottom figure),
represent upper limits.
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