COMMISSION 27 OF THE I. A. U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 3427

                                               Konkoly Observatory
                                               Budapest
                                               1 February 1990

                                               HU ISSN 0374 - 0676




                      Period change in AD CMi

  A period change of AD CMi was first reported by Jiang (1987)
and, in an independent way by Rodriguez et al. (1988). Although 
the two calculated values P =1.9(+/-0.1) * 10^-8(d/yr) and
P =1.1(+/-0.2) * 10^-8(d/yr) respectively, are slightly different, it is
clear that the period is now increasing.

  In order to establish the ephemeris for AD CMi we have put
together all the times of maxima reported by the above mentioned
authors. Furthermore, we have also considered one new light maximum 
from Langford (1976). Furthermore, a new set of observations 
was collected on February 1988, at the Sierra Nevada Observatory, 
in Spain, and two new times of light maximum have been
obtained by using the method described in Rodriguez et al. (1989).

  In column 2 of Table 1 are listed all the times of maxima available 
up to date. In the last column, the references are:
1) Abhyankar (1959), 2) Anderson et al. (1961), 3) Langford
(1976), 4) Epstein et al. (1973), 5) Balona et al. (1983), 6) Jiang
(1987), 7) Rodriguez et al. (1988) and 8) our new maxima (1988).
In total, times of 37 maxima (from 1959 to 1988) were used for
the determination of the ephemeris of the light curve of AD CMi
using the classical O-C method. We adopted an initial epoch of
T=2436601.8226 d and an initial period of P=0.12297431 d (from
Rodriguez et al., 1988). Resulting cycles E; are listed in the third
column of the Table. A least square fit of a linear ephemeris leads
to the following elements:


T0 = 2436601.8217 d
P0 = 0.12297447 d

Residuals (O-C), with respect to this linear ephemeris are shown


in the fourth column of the Table, and plotted in Figure 1. From
this figure it appears that a quadratic fit as


          Tmax = T0 + P0. E + A.E^2

and the following coefficients


          T0 = 2436601.8225 (+/-0.0002) d
          P0 = 0.12297426(+/-0.00000002) d

           A = 2.7d * 10^-12(+/-0.2)

      TABLE 1. Times of maxima of AD CMi

i     Ti (HJD)     Ei      (O-C)l     (O-C)r   Ref
      2100000. +   cycle    day        day

1     36601.8227   0        0.0010    0.0002   1
2     36602.8066   8        0.0011    0.0003   1
3     36802.9296   9        0.0011    0.0003   1
4     38604.8971   25       0.0011    0.0002   1
5     36627.7700   211      0.0007   -0.0001   1
6     36828.7638   219      0.0007   -0.0001   1
7     36629.7373   227      0.0004   -0.0004   1
8     36829.8602   228      0.0003   -0.0004   1
9     36931.762   2683     -0.0002   -0.0004   2
10    36932.747   2691      0.0010    0.0008   2
11    36934.836   2708     -0.0005   -0.0008   2
12    36969.762   2992      0.0007    0.0005   2
13    39202.729  21160     -0.0028   -0.0002   3
14    41010.6985 35852     -0.0040   -0.0005   4
15    43182.4297 53512     -0.0020    0.0011   5
16    43536.3494 56390     -0.0029    0.0000   5
17    43536.4727 56391     -0.0025    0.0003   5
18    44645.0877 65406     -0.0024   -0.0006   6
19    45766.3713 74524     -0.0001    0.0003   7
20    45768.3377 74540     -0.0013   -0.0009   7
21    45768.4406 74541     -0.0013   -0.0009   7
22    45771.4134 74565      0.0001    0.0006   7
23    45772.3961 74573     -0.0010   -0.0006   7
24    45772.6187 74574     -0.0010   -0.0010   7
25    46417.3991 79818      0.0009    0.0002   6
26    46418.2596 79825      0.0005   -0.0001   6
27    46418.3825 79828      0.0005   -0.0002   6
28    46419.3434 79833      0.0006   -0.0001   6
29    46419.3663 79834      0.0006   -0.0002   6
30    46443.1010 80027      0.0011    0.0004   6
31    46443.2243 80028      0.0014    0.0007   6
32    46443.3470 80029      0.0012    0.0005   6
33    46444.0850 80035      0.0013    0.0006   6
34    46444.2082 80036      0.0015    0.0008   6
35    46444.3312 80037      0.0016    0.0009   6
36    47219.4395 86340      0.0018   -0.0004   8
37    47220.4228 86348      0.0013   -0.0009   8



                              [FIGURE 1]

  Figure 1. O-C versus epoch diagram using the linear ephemeris

fit the data much better than the linear ephemeris in according
with earlier results obtained by Jiang (1987) and Rodriguez et al.
(1988). Second residuals (O-C)q listed in the fifth column in the
Table appear to be randomly distributed around zero showing that
the residuals (O-C)l can be well fitted by a parabola, indicating
that the pulsation period of this star is increasing at a rate of
P =1.6(+/-0.1) * 10E-8 (d/yr).


                E. RODRIGUEZ
                A. ROLLAND
                P. LOPEZ DE COCA
          Instituto de Astrofisica de Andalucia
            Apdo. 2144, Granada, Spain


REFERENCES

Abhyankar, K.D. 1959, Astrophys. J. 130, 834 [BIBCODE 1959ApJ...130..834A ]
Anderson, L.R. and McNamara, D.H. 1961, Publ. Astr. Soc. Pacific.
   94, 289 [BIBCODE 1960PASP...72..506A ]
Balona, L.A. and Stobie, R.S. 1983, South African Astron. Obs. 7,19 [BIBCODE 1983SAAOC...7...19B ]
Epstein, I. and Epstein, A.E.A. 1973, Astron. J. 78, 83 [BIBCODE 1973AJ.....78...83E ]
Jiang, S.Y. 1987, Chin. Astron. Astrophys. 11, 343 [BIBCODE 1987ChA&A..11..343J ]
Langford, W.R. 1976, Ph. Thesis, Brigham University [BIBCODE 1976PhDT.........1L ]
Rodriguez, E., Lopez de Coca, P., Rolland, A. and Garrido, R. 1989,
   Rev. Mex. Astron. Astrofis. (submitted)
Rodriguez, E., Rolland, A. and Lopez de Coca, P. 1988, Rev. Mex.
   Astron. Astrofis. 16, 7 [BIBCODE 1988RMxAA..16....7R ]