The field between 95˚ and 116˚ galactic longitude and −5˚ and 15˚ galactic latitude contains numerous HII regions. Among them Sh 2-131, Sh 2-132 and Sh 2-157 are the most prominent, associated with some very young open clusters. Several OB associations have been identified in this direction (Cep OB1, Cep OB2, Cep OB3, Cep OB5 and Cas OB2), some of which are well studied in terms of broad-band photometry (see Humphreys [1] and the references therein).

The goal of this investigation is to provide homogeneous distance and reddening estimates for as many young stars as possible in the studied coordinate range. We use the intermediate-band uvbyβ photometric system (Strömgren [2], Crawford & Mander [3]), since it allows reliable distance determination which helps distinguish among closely spaced groups along the line of sight (see for example Kaltcheva & Golev [4]). This study is aimed to provide the basis for a further detailed investigation of the interaction between the OB stars and the interstellar medium for this field.

The field is selected to cover the isolated large-scale feature seen in Hα between 95˚ and 116˚ galactic longitude. All uvbyβ data within this coordinate range was extracted from the catalog of Hauck & Mermilliod [5]. The sample contains 222 stars of spectral types O to B9 with complete uvbyβ photometry. The sample stars are presented in Figure 1. They are overplotted on an Hα map smoothed to 4 arcmin resolution to remove star residuals, Gaustad et al. [6], which is obtained via the SkyView VO interface (McGlynn et al. [7]).

The color excess E(b-y) for stars of luminosity classes (LC) III, IV and V was obtained via the Crawford’s [8] calibration. The calibration by Kilkenny & Whittet [9] was used for LC II, Ib, Iab and Ia. We used R = 3.18 and E(B − V) = E(b − y)/0.74 to obtain the corrected for reddening visual magnitude V₀. The calibration by Balona & Shobbrook [10] was applied to derive the absolute magnitude M_V for each star. For stars indicated as emission-line stars, β calculated from c₀ was used to calculate M_V. This procedure has been described in detail in earlier studies of star-forming fields based on uvbyβ photometry (see for example Kaltcheva & Hilditch [11]). Note that the uvbyβ photometric distances derived in this way are in excellent agreement with the recalculated Hipparcos data (Kaltcheva & Makarov [12]). In addition, the by Balona & Shobbrook [10] luminosity calibration has been

tested via the Hipparcos data and shown to be reliable (Kaltcheva & Knude [13], Torra et al. [14], Kaltcheva & Golev [15]). Note that in the uvbyβ system both the color excess and absolute magnitude calculations do not rely on a precise determination of spectral type and, to some extent, the luminosity class. This is because the calculations are carried on in the same way for all stars in a given spectral range (e.g. O-B9), depending on the LC for the color excess derivation only. The spectral and luminosity classes used in these calculations were extracted from the SIMBAD database and verified based on the classification [c₁] vs. [m₁] diagram (Strömgren [2] not shown here). The expected uncertainties in the derived distances are of the order of −13% to +15% for LC III-V, and −21% to +26% for LC I-II.

Table 1 (available in full from the authors upon request) summarizes the photometric data and the derived stellar parameters. The table includes stellar identifications, followed by spectral and luminosity type and uvbyβ photometric data, color excess and dereddened