Bright Northern BVRI Standards

Michael,
I have prepared this note mainly for amateur variable-star observers, but you may find it appropriate to post for the TASS folks. This is a major revision of the long bleat I sent out a couple of years ago to the 'vsnet' group. I have sent it to the Japanese 'vsnet' listserver again and also the AAVSO CCD discussion group (obviously the main target audiences), and have submitted it to the sci.astro.research moderator.
\Brian
January 19, 1997

Northern-hemisphere standard stars: why make a new list?

In March 1995 I sent out to 'vsnet' a long note containing a list of 42 BVRI standard stars of intermediate brightness (ranging from about mag. 5 down to mag. 8). This was by way of encouraging common use of standard photometric filter passbands among the amateur observers, and to provide a reliable list of standards for northern hemisphere observers with small telescopes. As most of you probably know, the AAVSO and other variable-star organizations do not accept CCD photometry done without filters. Unfiltered photometry simply cannot be merged with other data to get meaningful astrophysical results. Since several prominent 'vsnet' contributors report unfiltered photometry, I should note that such data is fine in the case of dwarf novae, at least in the case where you want to find out simply if the star is in outburst or not.

The well-known equatorial standard stars observed by Landolt are fine for many purposes. But because they appear quite low in the sky for many amateur observers, particularly Europeans, it is not possible to use them to determine good instrumental color transformations or for extinction. And even those of us at lower latitudes would like to have some stars more nearly overhead to determine atmospheric extinction. It turns out there is very little photometry really good of moderately bright northern stars on the well-established Cousins VRI system, and clearly a program to establish some new northern standards is needed to fill this gap.

In the last few weeks I have been prompted to re-examine the situation. After immersing myself fairly thoroughly in the Cousins VRI literature, I have compiled a somewhat more complete list of brighter stars for which published BVRI photometry could be fairly said to be good enough for use as "standards" (as compared with sequences around variable stars, say, which are not really standards). There are still far more equatorial stars than I would like, but any new set will have to be referenced to these higher-weight bona fide standards. The list of authors involved is quite short, the data coming mainly from Cousins himself, Landolt, Taylor's work on adjusting various sources to the Cousins system, and Taylor & Joner's own photometry, plus a few extraneous sources (such as myself) for some values. The Cousins and Landolt stars can be regarded as "primary" standards, and the remainder as "secondary" standards.

I'll outline the details of the star and data selection and so on later, but first I'd like to explain why such a list is even necessary. It will be convenient to discuss various topics in a question-and-answer form.

Frequently-asked Questions about Standard Stars

"What is the difference between the Johnson and Cousins R and I passbands?" The effective wavelengths are different, with the Cousins filters centered at shorter (bluer) wavelengths than Johnson's. Cousins R peaks near 6200A, but has a long redward tail, extending beyond 8000A; the Johnson R filter is nearly symmetrical and centered at about 6900A. Cousins I covers the range from about 7200A - 8500A, centered at about 7900A, whereas Johnson I has a broad passband from about 7500A out past 1 micron, centered near 8800A. See Figure 1 in Bessell (1983) for a graphic comparison. For what it's worth, the Cousins and Johnson V systems of magnitudes are (by design) identical within very small errors---no need to worry about V.
"I've been using the bright UBVRI standards out of the annual 'Astronomical Almanac'; what's wrong with these stars?" Plenty! Too much, in fact. The first problem is that VRI colors are on the original Johnson system, which has now fallen into disuse because of the better-defined and fainter Landolt standards. (The rise in detector sensitivity and increase in telescope apertures among professionals especially has meant that very few people could even observe the very bright Johnson standards without completely saturating or risking harm to their instruments.) This means if you measure V-R and/or R-I colors on the Johnson system, you will not be able to compare them with practically anyone else's numbers.
The Johnson "Almanac" stars have other problems as well. The Almanac data derive from a major publication by Johnson et al. (1966) containing an all-sky survey of bright stars. Although based on measurements using (among others) the original UBV filters and 1P21 photomultiplier---and hence in effect defining the system, the data there are noisy by contemporary standards, with rms scatter in the +/-0.03 range (Landolt's data have an internal precision of +/-0.005 mag.). In addition, compared to the Cousins system, the VRI colors show zero-point variations as a function of star color, with reddening (for hot stars), and even with Right Ascension. The latter effect appears in both V-R and R-I. It means that observations made at one season will be systematically bluer or redder from observations taken at another time. For instance, you observe a program star when it first comes up at dawn, and calibrate against standards somewhat higher in the sky to the west. Then at the end of the observing season for that star, you do some more observing, but calibrate now with stars east of the variable. With the Almanac standards, even if your data is perfect, your results would differ simply because the colors of the calibration stars were systematically different between the two sets of data. Not good!
Why hasn't anybody mentioned these problems before? The news is 10 to 20 years old: the large accidental errors were found by Barry et al. in 1977 and by Kunkel & Rydgren in 1979; the shifts as a function of RA were first found by Cousins in 1981; a more thorough analysis of all these problems can be found in Taylor (1986).
Obviously, the Almanac data should be avoided; the list is also in serious need of revision/replacement. It is possible to transform data between the Johnson and Cousins VRI systems, at least for stars of ordinary color. Again, see Taylor (1986) for the excruciating details.
As an additional aside, much of the data in the 1966 Johnson et al. paper was summarized in a famous article in the July 1965 issue of "Sky & Telescope" (Iriarte et al. 1965). These data were also once frequently cited by professional astronomers (who should have known better!) as having been used as standards---even though the article states explicitly that they are not, to wit: "It should be remembered that the new Catalina-Tonantzintla observations do not define the UBV system." Again, avoid this list as well.
"To get some fainter Johnson VRI standards, I've been using stars from Moffett & Barnes (see, for instance, Moffett & Barnes 1979). Are these OK?" The internal precision is lots better in these data than for the older Johnson et al. series. But again, they are on the Johnson system, reduced against the Johnson et al. 1996 paper. They thus also inherit the zero-point drift with Right Ascension. You needn't worry about the details in this case, however, because all the useful data from these papers and several others has been transformed to Cousins VRI in Taylor's 1986 paper (see his Tables 6, 7, and 8). Use Taylor's numbers instead of the originals.
"Neckel & Chini (1980) published a list of faint UBVRI standards that cover a wide range of colors and include some stars fairly far north. This list still gets widely used, too. How about those guys?" For their VRI data, Neckel & Chini (NC) used a Cousins-like tube/filters combination to obtain Johnson-system data, using the Iriarte et al. "Sky & Telescope" article for their standards, which we just trashed. There were bound to be problems. Taylor et al. (1989) obtained good quality Cousins VRI data for 54 of the 60 NC stars. They found the V magnitudes to have a strong systematic error as a function of V-R color; the full amplitude of the relationship is about 0.04 mag. between the bluest and reddest stars, although it is not so bad for stars of intermediate color. Again, probably because they used the Johnson data as calibration, the NC VRI colors also exhibit an RA drift, amounting to 0.06 mag. at maximum in R-I. Yow! Since Taylor et al. have obtained much better Cousins data for nearly all the NC stars, you can continue using these as standards, but with the values presented by Taylor et al. (see their Table II). I have included a few of these stars in the list below. That the NC stars had problems was not news even when Taylor et al. did their work: they were first pointed out by Bessell (1983).
"I was able to get a copy of Tarmo Oja's recent paper (Oja 1996), which contains Johnson-Cousins UBVRI observations of northern stars he reckons to be used as standards. Are you gonna trash these, too?" This paper summarizes a set of primary standards and other much-observed stars he's measured in the course of an extensive program lasting more than a decade. Since much of the work was done from Scandinavia, some quite far-north stars are included. Because a large number of observations is involved (some of the stars measured more than 100 times), these averaged results might be okay. Alas, the observations and reductions are only very sketchily described, and there is no statistical analysis in search of problems such as I've mentioned above, nor comparison with other work---stuff you want to see for results claiming to define standards. I have been able to compare his V data for a number of the fainter stars with reliable independent sources, and this suggests the V magnitudes are good, at least for stars of intermediate color (I was not able to test very blue or red stars). This is a good sign, but pending further checks, I don't yet have a "warm, fuzzy feeling" about Oja's numbers. Even so, I have added four of his stars to the table below.
"You've mentioned this RA zero-point drift problem several times. How do we know the same thing doesn't appear in the Landolt and Cousins data?" This has indeed been a concern. For many of the Landolt equatorial standards, "alternative" data is published by Menzies et al. (1991), based on observations from the South Africa Astronomical Observatory. These results were carefully tied to the Cousins E-region standards and have small internal errors. There are clear systematic differences between Landolt and the SAAO group arising from instrumental effects, but for the purposes of most amateur observing (i.e. from relatively poor photometric sites), the differences are "down in the noise". In making reductions with equatorial standards, choose one set of data or the other, don't average them.
When they compared their data to Landolt's, Menzies et al. found a disturbing trend as a function of RA in the V magnitudes (see Figure 3 in Menzies et al. 1991). Later comparison against a third homogeneous dataset showed that the problem appears to lie in the SAAO data, not in Landolt's (see the mea culpa in Cousins & Menzies 1993). This three-way intercomparison, by the way, also showed that the original Cousins E-region standards at -45 Dec do not have any detectable RA-drift problems. If you're a southern-hemisphere observer and managed to read this far, you should be using nothing else than these stars as standards (most recently defined by Menzies et al. 1989).
"Okay, you've convinced me I need to use high-quality standard stars and adopt the Cousins system for V-R and R-I (or V-I). What do I do about filters?" This whole business is very nicely covered in Mike Bessell's article in "CCD Astronomy" magazine, Fall 1995 issue, page 20. This describes the filter passbands, gives filter recipes for each, and lists (USA) suppliers of the filters.
The main concern here is to avoid interference filters whose bandpasses have steep sides, which lead to problems when transforming your data to the standard system. The litany of problems resulting from CCD data taken with such rectangular passbands is outlined in a series of publications by Bessell; particularly see Bessell (1990) for a list of earlier papers, and which also includes an earlier take on UBVRI filter prescriptions for CCDs. The colored- glass filters Bessell recommends greatly reduce such problems, and are much less expensive than interference filters.
This is probably as good a place as any to mention that if you want to determine even differential magnitudes in one filter, you need to observe in at least two. The reason is that no matter what you do vis-a-vis CCD chip, filters, or reductions, your instrumental color system will never match the original standard system perfectly. You will always need to make at least a small adjustment to your data to place them on the standard system. This is necessary even in differential photometry because of the differing colors of the comparison stars and the variable. This is usually done by finding the correction as a function of star color. The process is too involved to explain here in detail, but is well-covered in guides to doing photometry.
Well, which two should you choose? A natural choice for most CCD observing will be V and R: these provide a tie to familiar V magnitudes, and the R filter will take advantage of the peak wavelength sensitivity of the CCD chip, allowing you to go as faint as possible. You might also consider using V and I instead. The I passband is more useful on Miras and other red stars, and the added color baseline gives you a better handle on temperature changes in all variable stars. An I filter also is outside the range of the worst of light-pollution, so your observations will not be limited so much by city lights, but instead by the natural skyglow.

Star Selection for Primary and Secondary Standards

Since most observers are using small telescopes, and evidently have been using some quite bright stars to calibrate their data, the list includes only stars brighter than about V ~10, and most are brighter than V = 8. (The brightest has V = 5.2.) This makes them easy to find, and in general each star is much the brightest one in the field, so that identification is unambiguous.

The CCD exposure nomograms by Zissell (1996) for a typical CCD system on a 60cm (24-inch) telescope show that a 10-second exposure achieves a signal-to- noise ratio greater than 100 for stars brighter than about mag. 11 in V, R, and I. A smaller 25cm (10-inch) telescope more commonly used by amateurs will get the same results for stars about 1.5 magnitude brighter. Thus choosing standard stars between about mag. 6 and 10 seems a reasonable choice for small- telescope users. This allows exposures short enough so as not to consume much time on standards, but not so short as to risk shutter-timing errors nor to add scatter to the data due to atmospheric scintillation.

I first selected stars brighter than V = 7.5 from the main 1983 Landolt paper (Landolt 1983a), avoiding wide double stars (difficult to do aperture photometry on) and those having large uncertainty values, indicative of variability. A few stars were drawn from the unjustly neglected "instrument stability" paper by Landolt (1983b). These were supplemented by brighter stars from Taylor's (1986) summary of VRI colors for equatorial standards. As mentioned above, in this paper VRI photometry from many sources (e.g. Moffett & Barnes 1979; Crawford, Golson, & Landolt 1971) was transformed to the Cousins system. Because bright stars are relatively scarce in these lists, this initial set had several gaps in RA coverage. I thus added selected stars from Landolt (1983a) and Taylor between V = 7.5 and 8.0 to fill in both in RA and in color. Some good red-blue pairs are included as "extinction" stars (e.g. HD 30544 and 30545) as well as for determining rough color transformations. More exact color transformations should be done with stars throughout the color range.

To get additional stars farther north, I have scanned papers by Cousins and by Taylor & Joner. I chose Cousins stars north of +5 Dec, and several stars in the Hyades and Coma star clusters observed by Taylor & Joner. The particular stars selected in the two clusters are all mid-F type stars which served as comparisons for a decade-long study of variability among somewhat cooler solar-type stars in which I participated (see Radick et al. 1995 and Radick et al. 1990). These stars are constant at the 0.001 mag. level on the timescale of a decade. In another open cluster, M67, I have included two well-observed stars in the "dipper" asterism in the south side of the cluster. Unlike the fainter "dipper" stars, these two are isolated enough for use with telescopes of short focal length. Four northern Oja secondary standards are included as mentioned earlier. In several cases where the published V magnitudes from UBV photometry are not of high weight, I have opted to use V magnitudes determined by Erik Olsen from Stromgren photometry. These are tied directly to the Johnson et al. 1966 data, which closely define the system and are free of color and seasonal RA-drift effects.

The working list below contains stars from most parts of the HR diagram, including reddened hot stars, cool dwarfs, a few supergiants, and even a few extreme O subdwarfs used as spectrophotometric flux standards. All the cooler dwarfs selected have low chromospheric activity, so shouldn't be spotted variables (although my 12 years of photometry on HD 10476 shows that it is variable at the 0.01 mag. level over decadal timescales). Some known variables of very small amplitude are nevertheless retained; likewise some slightly variable M giants, kept in order to extend the color range.

The table is largely self-explanatory. I have used HD numbers in preference to all other designations. The star-name list is repeated at the bottom with notes added, including Selected Area and HR numbers, etc. The J2000 positions are from the PPM catalogue, and are given to 1s/0'.1 precision, sufficient to center a star in the typical CCD frame. Next come the V magnitudes and BVRI colors. The VRI colors are on the Cousins system. Some of the data are given to just two decimal places when the third decimal is either not available or I felt the precision was not justified. The spectral types were drawn from wide variety of sources, sought using the SIMBAD database. The final column shows the source of the numbers; the codes are explained at the bottom of the table.

Some other comments:

For many observers the most practical approach to using this list is to have previously determined color coefficients for your system using a large number of stars observed over several clear nights. Then assuming these values as constants, two or three stars can be used on any given night to set zero-points for a new "unknown" field. This avoids having to establish instrumental coefficients each night, which requires two or three dozen stars, and simply can't be done regularly from most sites.

Even if you use no filter, you should try to determine the color term of your system by using the red and blue stars in the list. Probably the best method would be to adjust your "wide-open" CCD magnitudes to the R scale as a function of V-R or R-I. Adjusting to V as a function of V-R or V-I might work as well for some CCDs. Of course, R = V - (V-R), and V-I = (V-R) + (R-I). Meanwhile, work on getting some filters for your system!

Finally, it should be noted once again that in principle there is no way to transform data for emission-line objects like novae and supernovae to any standard photometric scale based on ordinary stars. The spectra are simply too dissimilar to avoid systematic errors between different filter/detector combinations. The problem is most acute toward the blue, but workable with broadband filters in the red---as long as each system is well calibrated. This does not mean such data are not useful, but the results will be on a purely instrumental system that will differ for each observer.

Bright northern BVRI standards

Below is the table and notes. If you wish, you can click here to grab a copy of the table alone.

version:  5 January 1997

Name         RA  (2000)  Dec      V     B-V    V-R    R-I   MK       source
HD   315     0 07 44  -2 32.9   6.440 -0.145 -0.037 -0.064  B8IIISi  L83a
HD  5612     0 57 54 +13 41.8   6.32   0.90   0.462  0.421  G8III    J66/T86
HD  7615     1 16 28 +23 35.4   6.693  0.047  0.06  -0.01   A0       L83b
HD  8949     1 28 23  +7 57.7   6.205  1.12   0.559  0.490  K1III    C80/J66
HD 10476     1 42 30 +20 16.1   5.240  0.84   0.461  0.406  K1V      Olsen/T86
HD 11257     1 50 52 +11 02.6   5.927  0.30   0.199  0.193  F2Vwl    J66/T86
HD 14827     2 25 13 +55 15.3   7.633  0.045  0.028  0.066  A0II     Oja96
HD 16160     2 36 05  +6 53.2   5.801  0.987  0.578  0.485  K3-V     C80/C84
HD 18145     2 54 47  -0 02.9   6.528  1.048  0.529  0.497  G8II     T86
HD 18175     2 55 14  +0 26.2   7.033  1.129  0.572  0.526  K0II     T86
HD 18369     2 57 10  +0 26.9   6.628  0.327  0.193  0.191  F0IV     T86
HD 19525     3 08 39  +8 28.3   6.286  1.051  0.536  0.481  G9III    C80/C84
HD 22211     3 34 49  +6 25.1   6.487  0.634  0.357  0.339  G0       C80/C84
HD 23432     3 45 54 +24 33.3   5.780 -0.04   0.006 -0.027  B8V      K91/T86
HD 23441     3 46 03 +24 31.7   6.446 -0.02   0.007 -0.027  A0Vn     K91/T86
HD 23841     3 48 31  +9 38.8   6.689  1.233  0.663  0.612  K1III    C80/C84
HD 25102     3 59 40 +10 19.8   6.356  0.42   0.252  0.228  F5V      J66/T86
HD 27848     4 24 22 +17 04.7   6.962  0.443  0.267  0.250  F6V      Olsen/T89
HD 28406     4 29 30 +17 51.8   6.902  0.453  0.276  0.259  F6V      Olsen/T89
HD 29225     4 36 41 +15 52.2   6.636  0.433  0.263  0.249  F5V      Olsen/T89
HD 30197     4 46 17 +18 44.1   6.01   1.21   0.620  0.533  K4III    J66/T86
HD 30544     4 48 39  +3 39.0   7.316 -0.062 -0.016 -0.016  B9       T86
HD 30545     4 48 45  +3 35.3   6.031  1.207  0.598  0.565  K1III    T86
HD 31331     4 54 51  +0 28.0   5.992 -0.128 -0.046 -0.055  B5V      T86
HD 33647     5 11 41  +0 30.9   6.67  -0.07  -0.020 -0.046  B9Vn     J66/T86
HD 34317     5 16 41  +1 56.8   6.422 -0.02   0.015  0.009  A0V      J66/T86
HD 35215     5 24 28 +30 11.5   9.411  0.08   0.088  0.070  B1V      T89
HD 35407     5 24 36  +2 21.2   6.320 -0.15  -0.055 -0.092  B4IVn    J66/T86
HD 37334     5 37 37  -4 56.0   7.150 -0.160 -0.07  -0.09   B1.5V    L83b
HD 37352     5 39 15 +30 09.0   7.71   0.12   0.12   0.09   A0       L83b
HD 37557     5 40 36 +28 58.6   7.03   1.15   0.61   0.53   K0       L83b
HD 37981     5 42 58 +14 10.7   6.731  1.096  0.58   0.51   K1IV     L83b
HD 39632     5 54 13 +10 35.2   6.111  1.461  0.759  0.686  G9II     C80/C84
HD 40210     5 57 25  +0 01.6   6.905 -0.005  0.012  0.014  A0V      T86
HD 47240     6 37 53  +4 57.4   6.152  0.152  0.108  0.126  B1Ib     C80/C84
HD 48099     6 41 59  +6 20.7   6.349 -0.037  0.018  0.001  O6.5Ve   C80/C84
HD 50167     6 52 04  +1 15.1   7.861  1.535  0.826  0.757  K5       L83a
HD 268518    7 04 05 +20 35.8   7.579  0.614  0.352  0.353  G0       Oja96
HD 65079     7 57 04  +2 57.0   7.832 -0.182 -0.055 -0.075  B2Vne    L83a
HD 75012     8 47 35  +0 04.7   7.815  0.088  0.047  0.059  B9       T86
M67 F81      8 51 12 +11 45.4  10.027 -0.086 -0.032 -0.036  B8V      see note
M67 F170     8 51 30 +11 47.3   9.645  1.357  0.702  0.625  K3III    see note
HD 75700     8 51 49 +11 53.7   7.85   1.12   0.567  0.519  K0       TJ85
BD-00 2084   8 53 14  -0 43.5   9.150  1.276  0.649  0.553  K2       L92
HD 79097     9 11 51  -6 58.8   7.601  1.628  0.990  1.100  M0       L83a
HD 82106     9 29 55  +5 39.3   7.201  1.022  0.582  0.493  K3V      C80/C84
HD 84542     9 46 10  +6 42.5   5.807  1.636  0.921  0.991  M1.5III  C80/C84
HD 85990     9 55 35  -1 07.6   7.997  1.108  0.575  0.515  K0III    L83a
HD 86135     9 56 39  -0 27.7   7.835  1.485  0.795  0.728  K5       L83a
HD 94864    10 57 08  -0 18.7   6.877  0.421  0.250  0.243  F5       T86
HD 97991    11 16 12  -3 28.3   7.391 -0.227 -0.102 -0.140  B1V      T86
HD100600    11 34 43 +16 47.8   5.948 -0.158 -0.056 -0.100  B4V+B6   Jz66/T86
HD101906    11 43 47 +24 00.6   7.41   0.86   0.48   0.44   G2IV     L83b
HD102056    11 44 44 +28 40.2   7.02  -0.00  -0.00  -0.00   Am       L83b
HD103095    11 52 59 +37 43.1   6.427  0.753  0.460  0.437  G9Vwl    Olsen/T86
HD106542    12 15 14 +16 54.4   6.819  1.184  0.59   0.53   K2       L83b
HD106691    12 16 08 +25 45.6   8.083  0.407  0.238  0.244  F2V      Olsen/JT
HD107146    12 19 06 +16 32.9   7.028  0.602  0.33   0.31   G2V      L83b
HD107877    12 23 41 +26 58.8   8.364  0.443  0.264  0.257  F5V      Olsen/JT
HD108154    12 25 22 +23 13.7   8.569  0.453  0.270  0.269  F8V      Olsen/JT
HD108976    12 31 03 +27 43.8   8.554  0.475  0.275  0.271  F7V      Olsen/JT
BD+35 2349  12 32 45 +34 35.0   9.53   1.32   0.698  0.613  K2III    Oja96
BD+35 2352  12 34 24 +34 19.9  10.19   0.99   0.533  0.475  K0III    Oja96
BD+25 2534  12 37 23 +25 04.0  10.510 -0.29  -0.145 -0.17   sdO      T89
HD111165    12 47 15  +7 00.5   8.461  1.169  0.568  0.506  K0       T86
HD111397    12 48 54 +14 07.4   5.70   0.02   0.007  0.018  A1V      J66/T86
HD118330    13 36 15  -0 55.9   7.062  0.528  0.313  0.311  F8       L83a
BD+30 2431  13 38 25 +29 22.0  10.055 -0.14  -0.065 -0.074  sdB      T89
HD122563    14 02 32  +9 41.2   6.196  0.912  0.550  0.545  G8:II:   C80/C84
HD126271    14 24 18  +8 05.1   6.189  1.203  0.630  0.555  K4III    C80/C84
HD129956    14 45 30  +0 43.0   5.685 -0.022 -0.010 -0.003  B9.5V    T86
HD134047    15 07 40  +5 29.9   6.166  0.947  0.487  0.451  G7IIIa   C80/C84
HD139195    15 36 30 +10 00.6   5.265  0.945  0.480  0.440  K0IIICN  C80
HD139137    15 36 34  -0 33.7   6.509  0.725  0.431  0.412  G8III+A5 T86
HD139308    15 37 29  -0 53.1   7.779  1.275  0.663  0.585  K0III    L83a
HD139590    15 39 01  -0 18.7   7.500  0.543  0.312  0.297  G0V      L83a
HD140775    15 45 23  +5 26.8   5.578  0.04   0.019  0.014  A0V      J66/T86
HD140873    15 46 06  -1 48.3   5.393 -0.032  0.000 -0.009  B8III    T86
HD149845    16 37 21  -0 24.8   7.964  1.303  0.682  0.589  K2       L83a
HD157881    17 25 45  +2 06.7   7.540  1.356  0.854  0.768  K7V      L83a
HD160233    17 38 41  +4 20.2   9.095 -0.054 -0.003 -0.023  B1V      L83a
HD161198    17 43 16 +21 36.5   7.521  0.745  0.45   0.42   G8V      L83b
HD161223    17 44 04  +6 03.7   7.435  0.326  0.22   0.24   A2       L83b
HD161242    17 44 13  +5 15.0   7.806  1.284  0.661  0.637  K2       T86
HD161817    17 46 41 +25 45.0   6.982  0.147  0.12   0.14   A7wl     L83b
BD+04 3508  17 47 33  +4 50.4   9.326  1.753  0.974  0.900  K5       L83b
HD163153    17 54 58  -7 44.0   6.926  0.759  0.41   0.35   G8IV     L83b
HD172365    18 39 37  +5 15.9   6.375  0.79   0.435  0.416  F8Ib-II  C80
HD172651    18 41 27  +0 33.9   7.474  1.449  0.767  0.681  K2       L83a
HD172829    18 42 18  +0 09.3   8.447  2.002  1.186  1.120  K5III    L83a
HD175544    18 55 47  +0 15.9   7.395  0.107  0.074  0.077  B2V      L83a
HD180028    19 14 45  +6 02.9   6.934  0.837  0.475  0.465  F6Ib     C80/C84
HD181122    19 18 53  +9 37.1   6.311  1.067  0.537  0.505  G9III    C80/C84
HD185025    19 37 16  +0 11.0   8.963  0.206  0.119  0.144  A0       L92
HD185297    19 38 22  +0 20.7   7.216  0.278  0.154  0.166  A7IV     L83a
HD186408    19 41 49 +50 31.5   5.980  0.648  0.357  0.341  G1.5V    Olsen/T86
HD186427    19 41 52 +50 31.1   6.235  0.660  0.363  0.343  G2.5V    Olsen/T86
HD186293    19 43 05  +9 29.4   7.833  1.160  0.575  0.525  K0Ib     C80/C84
HD186312    19 43 16  +9 29.8   7.856  1.458  0.765  0.695  K3II     C80/C84
HD186535    19 44 41  +8 43.6   6.419  0.952  0.482  0.450  G8III    C80/C84
HD195919    20 33 18 +27 27.4   8.981  0.05   0.031  0.038  A2       T89
HD196426    20 37 18  +0 05.8   6.206 -0.087 -0.039 -0.044  B8IIIp   T86
HD196573    20 38 16  +1 01.0   7.885  1.641  0.931  0.955  K5       L83a
HD199280    20 56 18  -3 33.7   6.566 -0.076 -0.034 -0.043  B8Vn     L83a
HD200340    21 03 00  -0 55.5   6.498 -0.099 -0.037 -0.045  B6V      L83a
HD200644    21 04 35  +5 30.2   5.593  1.651  0.860  0.785  K5III    C80/C84
HD205556    21 35 56  +5 28.6   8.301 -0.054 -0.021 -0.032  B9       L83a
HD205584    21 36 14  +6 08.2   7.711  1.264  0.617  0.579  K2       T86
BD+28 4211  21 51 11 +28 51.9  10.53  -0.34  -0.147 -0.17   sdO      J53/T89
HD209905    22 06 39  +2 26.4   6.496 -0.068 -0.011 -0.036  B9       T86
HD215077    22 42 43  +0 04.3   7.177  0.367  0.224  0.230  F0       T86
HD215093    22 42 49  +0 13.9   6.969  0.311  0.187  0.189  F0       L83a
HD217014    22 57 28 +20 46.1   5.455  0.67   0.373  0.326  G2.5IV   Olsen/T86
HD218155    23 05 33 +14 57.6   6.783  0.004 -0.01  -0.01   A0V      L83b
HD218537    23 07 48 +63 38.0   6.25  -0.01   0.025 -0.030  B3V      J66/T86
HD219134    23 13 17 +57 10.1   5.57   1.010  0.584  0.478  K3V      J66/T86
HD223963    23 54 03  -9 17.4   7.200  1.581  0.91   0.95   M0III    L83b
HD224155    23 55 38  +8 13.4   6.818 -0.003 -0.015 -0.010  A0V      C80/C84

sources:  C80 = Cousins 1980, C84 = Cousins 1984,
          L83a = Landolt 1983a, L83b = Landolt 1983b, L92 = Landolt 1992;
          T86 = Taylor 1986, T89 = Taylor et al. 1989 ;
          Jz66 = Jerzykiewicz 1966, J66 = Johnson et al. 1966;
          K91 = Kornilov et al 1991; TJ85 = Taylor & Joner 1985;
          GO76 = Gronbech & Olsen 1976, Olsen = various pubs by Olsen;
          Oja96 = Oja 1996.


Notes:
HD   315    HR 11.
HD  5612    HR 276.
HD  7615   
HD  8949    HR 426 = NSV 519. the brighter of a wide pair:  BD+07 214 at 1'.1,
            V=8.0, G0.
HD 10476    HR 493 = 107 Psc. large proper motion.
HD 11257    HR 534. V from K91+AT95.
HD 14827
HD 16160    HR 753. large proper motion.
HD 18145    SA 94-32.
HD 18175    SA 94-293.
HD 18369    SA 94-319.
HD 19525    HR 942.
HD 22211    HR 1089.
HD 23432    HR 1151 = 21 Tau = Asterope in Pleiades.
HD 23441    HR 1152 = 22 Tau in Pleiades.
HD 23841
HD 25102    HR 1233. V from K91.
HD 27848    vB 51 in Hyades.
HD 28406    vB 78 in Hyades.
HD 29225    vB 101 in Hyades.
HD 30197    HR 1517, near open cluster NGC 1647.
HD 30544   
HD 30545    HR 1534.
HD 31331    HR 1574 = SA 96-837.
HD 33647    HR 1690 = V1085 Ori (very small amplitude). V from K91+GO76.
HD 34317    HR 1724. V from GO76.
HD 35215    B-V from Hiltner (1956).
HD 35407    HR 1786. V from GO76.
HD 37334    NSV 2471, probably slightly variable in V, but colors stable.
HD 37352
HD 37557
HD 37981  
HD 39632    HR 2048.
HD 40210    SA 97-257.
HD 47240    HR 2432.
HD 48099    HR 2467.
HD 50167    ADS 5533: sep. ~2" with large delta-mag.
HD 268518
HD 65079 
HD 75012    northern star of a wide pair.
M67 F81     blue straggler in M67. VRI from Joner & Taylor 1990
            (PASP 102, 1004), B-V from Montgomery et al. 1993 (AJ 106, 181).
M67 F170    BD+12 1926 (sic, this BD name applies to the entire cluster).
            V from BSkiff, BVRI colors as for M67 F81.
HD 75700    bright field star on northeast side of M67. BV data from Eggen
            (1964 ApJ 140,130).
BD-00 2084  SA 100-162.
HD 79097    possibly slightly variable in V, but colors stable.
HD 82106    bright, large proper motion star not in PPM.
HD 84542    HR 3876; slightly variable in V, but colors stable.
HD 85990    SA 101-24.
HD 86135    SA 101-333.
HD 94864    SA 102-1085.
HD 97991    also V = 7.394, B-V = -0.224 (C84).
HD100600    HR 4456.
HD101906
HD102056
HD103095    HR 4550. V from Olsen, B-V from Jz66. very high proper motion.
HD106542    
HD106691    in Coma star cluster.
HD107146
HD107877    in Coma star cluster.
HD108154    in Coma star cluster.
HD108976    in Coma star cluster.
BD+25 2534  Feige 66; B-V adopted from Colina & Bohlin 1994 (AJ 108, 1931).
BD+30 2431  Feige 86; B-V is mean of several published values.
HD111133    HR 4854. also V = 6.327, B-V = -0.051 (C84).
HD111165    also V = 8.465, B-V = 1.167 (C84).
HD111397    HR 4865 = 29 Com.
HD118330    SA 105-214.
HD122563    HR 5270. extreme metal-weak giant.
HD126271    HR 5394 = NSV 6655.
HD129956    108 Vir = HR 5501.
HD134047    HR 5631.
HD139137    14 Ser = HR 5799 = SA 107-298. composite spectrum.
HD139195    HR 5802 = 16 Ser.
HD139308    SA 107-35.
HD139590    SA 107-595.
HD140775    HR 5859. V from GO76.
HD140873    25 Ser = HR 5863.
HD149845    SA 108-827.
HD157881    large proper motion.
HD160233
HD161198
HD161223    in region of open cluster IC 4665.
HD161242    in region of open cluster IC 4665.
HD161817
BD+04 3508  
HD163153   
HD172365    HR 7008 in open cluster IC 4756. B-V from Cousins 1965
            (MNSSA 24, 120).
HD172651    SA 110-471.
HD172829    HK Aquilae (constant) = SA 110-353. the reddest Landolt standard
            brighter than V mag. 10.
HD175544  
HD180028
HD181122    HR 7325.
HD185025    SA 111-773.
HD185297    SA 111-1496 = ADS 12708: sep. ~1".
HD186408    HR 7503 = 16 Cyg A. B-V from USNO.
HD186427    HR 7504 = 16 Cyg B. B-V from USNO.
HD186293    preceding of two stars.
HD186312    following of two stars.
HD186535
HD195919    B-V uncertain.
HD196426    HR 7878.
HD196573  
HD199280    HR 8014.
HD200340    HR 8054.
HD200644    HR 8066 = 3 Equ.
HD205556
HD205584
BD+28 4211  
HD209905  
HD215077    SA 114-69.
HD215093    SA 114-172.
HD217014    HR 8729 = 51 Peg. B-V from J66.
HD218155   
HD218537    HR 8808.
HD219134    HR 8832.
HD223963 
HD224155    B-V uncertain.

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Bessell, M. S.  1983, Publ. Astr. Soc. Pac. 95, 480.
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Cousins, A. J., and Menzies, J. W.  1993, in "Precision Photometry", Kilkenny
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Cousins, A. W.  1980, South Africa Astr. Obs. Circ. no. 5, 234
Cousins, A. W.  1981, Mon. Not. Astr. Soc. South Africa, 40, 37.
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Crawford, D. L., Golson, J. C., and Landolt, A. U.  1971, Publ. Astr. Soc. Pac.
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Iriarte, B., et al.  1965, Sky & Telescope, 30, 21 (July 1965).
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Menzies, J. W., et al.  1989, South Africa Astr. Obs. Circ. 13, 1.
Menzies, J. W., et al.  1991, Mon. Not. Roy. Astr. Soc. 248, 652.
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Radick, R. R., Lockwood, G. W., Skiff, B. A., and Thompson, D. T.  1995,
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