Following the traditional approach developed by Sandage & Tammann
(1974) and de Vaucouleurs (1978), we use the brightest
blue (V-I<+0.5) and red (V-I>+2.0) stars as distance indicators to the
galaxies. The photometric distance modulus, , was derived via the
mean apparent magnitude of three the brightest blue stars, <B(3B)>, from
where is the total apparent magnitude of the galaxy, and AB is the foreground galactic extinction. Relation (1) reflects well the known correlation between the luminosity of blue supergiants and the luminosity of their parent galaxy. Its numerical coefficients were calibrated by Piotto et al. (1992) and Karachentsev & Tikhonov (1994) using galaxies with known distances from Cepheids. To derive B magnitudes we use the empirical relation.
which is valid in general for Landolt's stars.
For deriving a modulus from red supergiants de Vaucouleurs (1978) recommended the use of their magnitude , irrespective of the luminosity of the parent galaxy. We applied this rule to all five galaxies observed.
Figure 1: The distribution of galaxies in the IC 342/Maffei complex in galactic coordinates. The open circles represent galaxies with radial velocities , the crosses correspond to other probable members of the complex. The inclined solid line is the Supergalactic equator
According to RC 3 (de Vaucouleurs et al. 1991) this irregular galaxy of Sm type has a standard angular diameter of 5.5 arcmin. A reproduction of its central part in the I-band is presented in Fig. 2 (click here). Applying the ALLSTAR programme, we carried out the photometry of 568 stars seen on both CCD frames and having the image parameters: SHARPCHI, and , where is a formal error of the V-magnitude. SHARP and CHI are measures of the starts shape and the goodness of fit, respectively, in the reductions. SHARP is a measure of the difference beetween the observed width of the object and the width of the psf model. The results of our photometry are given in Table 2. Its columns contain: (1) -- the star number, (2) and (3) -- the star coordinates expressed in pixels, (4) -- the V magnitude, (5) -- the colour index V-I, (6) -- the image parameter, SHARP.
Figure 2: The central part of UGCA 105 in the I band. The size of the CCD frame is 3.0 by 3.0 arcmin. North at top, East on the left
Figure 3 (click here) shows the "Colour-Magnitude'' diagram derived from these data. The brightest stars with V<20.5 and "neutral'' colour 0.7<V-I<2.2 are evidently foreground stars. The population of the brightest blue stars of the galaxy itself appears in the region of V>22.5 and V-I<0.6 in good agreement with the data by Tikhonov et al. (1992). Among them we select stars ##459, 226, and 261 as the brightest blue supergiant candidates, excluding from the consideration two cases, ##20 and 449 which have not sharp stellar images. Their mean apparent magnitude and colour are or and .
To determine the distance modulus from relation (1), we adopted for the total magnitude of the galaxy (Huchtmeier & Richter 1986), and for the galactic extinction (Burstein & Heiles 1984).
Note, UGCA 105 is quoted to be fainter in the RC3 . However, the photometric data by Krismer et al. (1995) and also our measurements fit well the previous magnitude. With our adopted parameters the distance modulus of UGCA 105 from blue stars is .
Among the red stars with V-I>2.5 the three brightest ones, #149, 322 and 227, have , that gives us the modulus of . The mean of the two estimates, , corresponds to a galaxy distance of in agreement with the earlier value of 3.31 Mpc given by Tikhonov et al. (1992). Comparing new (CCD) and old (photographic) measurements of the individual stars, we obtain the average difference in their zero-point
Figure 3: Colour-Magnitude diagram for 568 stars in UGCA 105
This irregular dwarf system with an angular diameter of has the lowest radial velocity among all the galaxies of the complex. Figure 4 (click here) reproduces its CCD frame obtained in the I band. The total magnitude of UGCA 92 is rather controversial. The catalog RC3 gives an apparent magnitude of , but in the catalog of Karachentseva & Sharina (1987) its magnitude is . According to the CCD photometry by Karachentseva et al. (1996) the galaxy has and . From present measurements after corrections for the Galactic stars the total magnitude and total colour of UGCA 92 are , , or and .
Figure 4: UGCA 92 in the I band. The size and the orientation of the frame are the same as previously
The results of our photometry of 184 stars are presented in Table 3, which is structured in the same way as Table 2. Among them 100 stars, situated inside the visible boundary of the galaxy, are indicated by "1'' in the last column. Figure 5 (click here) shows the Colour-Magnitude diagram based on these data. The red colour of many stars is caused obviously by the strong interstellar extinction. We estimated the absorption value, AB, from the galaxy colour. Adopting for an irregular type galaxy the mean true colour, (RC3), we obtain a colour excess of or . The brightest blue stars belonging to the galaxy itself are easily distinguished from the foreground stars. For the three brightest, # 82, 57 and 117 we obtain from relation (2) the mean: and , which gives the distance modulus of or .
From the C-M diagram it appears that the brightest red supergiants of the galaxy may have , . However, to distinguish them from foreground stars is a difficult task. Comparing the present photometry of individual stars with our old CCD data (Karachentsev et al. 1994), we find a systematic difference, , the reason of which remains unclear to us.
|UGCA 86||V||600 s||Feb. 6, 1995|
|UGCA 92||V||600 s||Feb. 6, 1995|
|UGCA 105||V||600 s||Feb. 6, 1995|
|NGC 1569||V||300 s||Feb. 7, 1995|
|Cas 1||V||600 s||Feb. 5, 1995|
The dwarf galaxy UGCA 86 with its radial velocity and standard angular diameter remains still the only indisputable satellite of the spiral IC 342. Figure 6 (click here) reproduces a CCD frame in the I band, covering the central part of UGCA 86 and also its bright southern concentration (= VIIZw9). According to Huchtmeier & Richter (1986) the total magnitude of UGCA 86 is known with a low accuracy and corresponds to .
To estimate the interstellar extinction in the direction to UGCA 86 we measured the colours of the two brightest parts: the central one and the southern. The mean value for them, corresponds to , that yields the colour excess E(B-V)=+0.91 and assuming a the typical intrinsic colour for an irregular galaxy, .
Figure 5: Colour-Magnitude diagram for UGCA 92. the stars inside and outside the galaxy body are indicated by open circles and crosses, respectively
Figure 6: The central part of UGCA 86 (above) and the bright southern superassociation (the lower left corner) in the I band
The results of ALLSTAR photometry for 444 stars are presented in Table 4 and in Fig. 7 (click here). The stars which are situated within the region of the bright southern knot are indicated in the last column with the number "0'', and by open circles in the C-M diagram. It is evident from Fig. 7 (click here) that the majority of the brightest "blue'' stars are concentrated just toward the southern complex. After avoiding some stars with V-I<0.5, whose photometry is affected by neighbouring diffuse objects, we selected the stars and 226 as the brightest blue supergiant candidates. Their mean apparent magnitude and colour are and Then the galaxy distance modulus is 27.26 assuming and .
Figure 7: Colour-Magnitude diagram for the southern concentration (open circles) and for the rest of the field of UGCA 86 (crosses)
Unlike blue stars, the red ones with colour V-I>3.1 are scattered more or less randomly over the whole galaxy body which makes it difficult to distinguish them from foreground stars. Adopting the stars #180, 94 and 40 with and as the red supergiant candidates we obtain a modulus of . The mean of the two estimates, , corresponds to a distance of , which exceeds appreciably the old estimate, 1.86 Mpc, by Karachentsev & Tikhonov (1993). Both these estimates agree quite well with the mean distance of IC 342 (). The difference between the new and the old photometric zero-points is negligible, , but the increase of the distance estimate is rather caused by a new selection of blue and red stars for the supergiants of the galaxy.
This peculiar galaxy with has been studied by many authors (Ables 1971; Arp & Sandage 1985; Karachentsev et al. 1994; Krismer et al. 1995). The high brightness gradient across NGC 1569 and a presence of dusty furrows in its body make stellar photometry very hard. The galaxy image in the I band is shown in Fig. 8 (click here). Its upper part reproduces one half of the original frame, and the lower one shows the same part of the galaxy after subtracting a frame smoothed with a window of , allowing a filtering of extended emission or unresolved stars. An application of the ALLSTAR package allowed us to perform the photometry of more than 500 stars inside the galaxy as well as arround it. However, a lot of stars, especially within its central part, were excluded due to the condition SHARP >2. The results of the photometry for the remainding 173 stars are given in Table 5, which contains also R magnitudes measured from a short exposure frame. Foreground stars, situated on the opposite (southern) half of the CCD frame, are indicated by the number "1''. The distribution of stars in the plane V vs. V-I is shown in Fig. 9 (click here). The stars from the northern and southern halfs of the CCD frame are noted by open circles and crosses, respectively. In this diagram we plot also 113 stars from the central part of NGC 1569, measured with the Hubble Space Telescope (O'Connel et al. 1994). These data fit each other quite well.
In contrast to the galaxies considered previously, NGC 1569 has no sharp left "shoulder'' in its C-M diagram, caused by a population of blue supergiants. Because of this, a distance modulus of the galaxy cannot be derived accurately.
|NGC 1560||-36||9.8||12.16||1.13||125||27.37||7.7||2.8||(KTGBS, 91)|
|Maffei 2||-2||3.8:||16.0||8.2||305||26.77||11.9||5.2||(TK, 94)|
|IC 342||+33||20.9||9.1||2.56||151||27.29||29.7||1.9:||(KT, 93)|
|Cam B||+75||2.2||16.1||1.5:||20||-||1.9||0.9||(HKK, 97)|
|Dwing 2||+94||1.0:||20.5:||9:||100||-||6.2||3.4||(BVKH, 96)|
|Dwing 1||+110||2.0||19:||10:||188||-||16.1||2.8||(BVKH, 96)|
|MB 1||+189||2.4||20.5:||9:||60||-||21.4||1.5||(MB, 95),|
|Footnotes: 1) The original estimate, , is reduced to 2.98 Mpc because of a new|
|value of AB; 2) The original distance estimate, , is corrected for a contamination|
|of brightest blue stars from compact HII regions.|
Figure 8: NGC 1569 in the I band. a) Southern half of the original frame, b) the same part after subtracting the frame smoothed with a window of
Adopting the stars #18, 50 and 70 as the three brightest blue supergiant candidates, we obtain for them and or . Using the total magnitude of the galaxy, , and an extinction of (RC3) this magnitude gives a modulus of in a good agreement with the estimate of by Karachentsev et al. (1994). It should be noted, however, that we did not find suitable red supergiant candidates based on their colour (V-I>2.6) and magnitude . In comparison with the results of aperture photometry (Karachentsev et al. 1994), the ALLSTAR photometry data for NGC 1569 reveal a systematic difference on faint magnitudes, which is probably related to significant brightness inhomogeneities over the galaxy.
Figure 9: V vs. (V-I) diagram for NGC 1569. Open circles corresponde to stars measured in the main body of the galaxy, crosses indicate foreground stars, open squares represent the stars in the central region of the galaxy measured with the Hubble Space Telescope by O'Connel et al. (1994)
This irregularly shaped galaxy with a low radial velocity of (Huchtmeier et al. 1995) is situated in a zone of strong galactic absorption. Figure 10 (click here) shows its CCD image in the I band. The results of our ALLSTAR photometry for 231 stars in the whole CCD frame are presented in Table 6. The colour-magnitude diagram, V versus (V-I), is shown in Fig. 11 (click here). The stars, which are located within the galaxy boundary, are indicated by number "1'' in the last column of Table 6 and by open circles in Fig. 11 (click here).
Figure 10: CCD image of Cassiopeia 1 in the I band
Figure 11: V vs. (V-I) diagram for Cas 1. Stars within the galaxy body are indicated by open squares the remainder of the frame stars are noted by crosses
It is evident from the C-M diagram that most moderately bright stars with are foreground stars affected by galactic reddening. In fact, a stellar population of Cas 1 itself can only be recognized with confidence in the region of . Taking as the brightest blue supergiant candidates the stars #138, 89 and 73, we obtain for them and or and .
Based on the CCD aperture photometry of the galaxy in V and I bands we obtain for Cas 1 a total apparent magnitude, , and or and . If the intrinsic colour of irregular type galaxies is adopted for cas 1, (B-V)0=0.36, we obtain a galactic extinction of Note that these data agree well with the quantities, , and , derived for Cas 1 by Tikhonov (1996). A substitution of the measured parameters into Eq. (1) gives us the distance modulus of Cas 1, or .