\documentstyle[twoside, epsf, hyperref]{article}
\input ibvs3.sty
\begin{document}
\IBVSheadDOI{63}{6236}{7 February 2018}

\IBVStitle{Revised coordinates of variable stars in Cassiopeia}


\IBVSauth{NESCI, R.}

\IBVSinsto{INAF/IAPS, via Fosso del Cavaliere 100, 00133 Roma, Italy, e-mail: roberto.nesci@iaps.inaf.it}

\GCVSobj{V508 Per}
\GCVSobj{V647 Cas}
\GCVSobj{V670 Cas}
\GCVSobj{V671 Cas}
\GCVSobj{V672 Cas}
\GCVSobj{V673 Cas}
\GCVSobj{V674 Cas}
\GCVSobj{V675 Cas}
\GCVSobj{V677 Cas}
\GCVSobj{V678 Cas} 
\GCVSobj{V679 Cas}
\GCVSobj{V680 Cas}
\GCVSobj{V681 Cas}
\GCVSobj{V682 Cas}
\GCVSobj{V683 Cas}
\GCVSobj{V684 Cas}
\GCVSobj{V685 Cas} 
\GCVSobj{V686 Cas}
\GCVSobj{V687 Cas} 
\GCVSobj{V688 Cas} 
\GCVSobj{V689 Cas}
\GCVSobj{V690 Cas}
\GCVSobj{V691 Cas} 
\GCVSobj{V692 Cas} 
\GCVSobj{V693 Cas}
\GCVSobj{V694 Cas} 
\GCVSobj{V695 Cas} 
\GCVSobj{V696 Cas} 
\GCVSobj{V697 Cas}
\GCVSobj{V698 Cas}
\GCVSobj{V699 Cas}
\GCVSobj{V700 Cas} 
\GCVSobj{V703 Cas}
\GCVSobj{V725 Cas}
\GCVSobj{V726 Cas}

\IBVSkey{astrometry}


\IBVSabs{The identification of the variable stars published on IBVS \#3573 has ben revised on the basis of the original (unpublished) finding charts. Cross check with the 2MASS catalog has been made to get more accurate coordinates and to confirm their nature from their $J-H$, $H-K$ colors. The Mira stars, given their known periods, could be used with the astrometric parallaxes of the forthcoming Gaia catalog to improve the Period-Luminosity relation.}

\begintext

\section {Introduction}
Mira stars are among the brightest star in a stellar population, and their absolute luminosity is fairly related to their pulsation period, so that are useful as standard candles to derive the distances of nearby galaxies.

A list of red variables, including a number of Miras, in a field centered on IC 1805, was published by Gasperoni, Maffei and Tosti (1991, IBVS \#3573), giving a measure of their periods on the basis of 7 years of observations using infrared (I-N + RG5) and blue (103aO) Schmidt plates of the Asiago Observatory.

This variable stars sample is statistically well defined, being magnitude limited and followed with 75 plates along 7 years. Gasperoni et al. (1991) did not publish finding charts but only coordinates at B1950, with arcmin approximation, rather poor for a safe identification near the galactic plane. Based on that paper, the stars were imported in the General Catalog of Variable Stars (Samus et al. 2017)  by Samus et al. (2003). The individual stars can be searched in SIMBAD by their original provisional name (SV* Mxxx) or by coordinates. They can also be searched in the VSX database, but only with the variable name or the coordinates, and the historic link to Gasperoni et al. (1991) is generally not present.

In the course of a larger on-going research on the Mira stars in Cassiopeia, I found for some of these stars strong inconsistencies between the optical and near infrared ($JHK$) magnitudes available from cross correlation of the GCVS and 2MASS (Cutri et al. 2003) catalogs, suggesting that some misidentifications have occurred. As a matter of fact, most of these stars are not referred by any paper (besides the discovery one) in the SIMBAD or ADS databases.

\section{Identification}
In the family archive of the late prof. Paolo Maffei ({\tt http://www.archiviomaffei.org}) I was able to recover the original paper enlargements of the  Asiago plates, with pencil annotations by Maffei of the detected variables and comparison sequences, so it was possible to check for all the stars their actual positions. I also found the two original thesis works (unpublished) of the two Maffei's students V. Gasperoni and G. Tosti  on the stars of this field.
Comparison of the finding charts with the Digitized Sky Survey infrared plates, available on-line from the Space Telescope Science Institute ({\tt http://archive.stsci.edu/cgi-bin/dss\_plate\_finder}), and with the 2MASS catalog and images, available from SIMBAD ({\tt http://simbad.u-strasbg.fr/simbad/}), and IRSA database ({\tt http://irsa.ipac.caltech.edu/}) allowed to perform a satisfactory identification for all the variables listed in Gasperoni et al. (1991) with a 2MASS counterpart.

In some cases the coordinates differences between Gasperoni et al. (1991) (precession corrected) and the actual coordinates were small, compatible with the quoted accuracy, but often they were rather large, several arcmin! Two stars have outstanding errors: M279 (presently identified in the GCVS as V0687 Cas) and M289 (identified in the GCVS as V0685 Cas).

In the case of  the SR variable M279 the published coordinates are 187 arcmin (3 degrees !) off from the position in the finding chart: the finding chart says that it must be associated to IRAS 02205+6014, a bright and very red star. At the coordinates of M279 published in Gasperoni et al. (1991) the CGVS reports V0676 Cas, but nothing similar to a red star is nearby. In Maffei's finding charts no variable star is reported near the published coordinates.

Similarly dramatic is the situation of the SR variable M289, which is 169 arcmin (again about 3 degrees) off from the published position: at the finding chart position there is a bright and red source in 2MASS, as should be for a SR variable. At this position the VSX catalog reports a low amplitude variable, NSVS 1890163. On his thesis, G. Tosti reports large irregularities in the light curve of this star, which prevented to define a time scale for its variability: the variability amplitude, 0.8 mag, is similar to that reported in the NSVS.
The associated name in GCVS is V0685 Cas, but its position corresponds to a rather bright and blue star ($B=13.188$, $V=12.697$, $B-V=0.49$ in the UCAC4 catalog) clearly inconsistent with the Maffei's variable because it is reported to be always below the detection limit ($B\sim18$ mag) in the Asiago blue plates. Clearly NSVS 1890163 is the actual identification of M289. 

I tried to understand from the documents in Maffei's archive how such large errors for these two stars could arise. In Tosti's thesis no coordinates are given, while in Gasperoni's one the coordinates are given as published in Gasperoni et al. (1991): the most likely explanation is therefore that the misprints in the thesis were carried on in the article. 

\section{Results}

Table 1 lists for each star the Maffei's provisional name and the B1950 coordinates as reported in Gasperoni et al. (1991), the J2000 coordinates of the actual 2MASS counterpart as derived from Maffei's original finding charts, the present designation in SIMBAD, the distance between the old (precessed to J2000) and the new position in arcmin. Only in 9 cases the coordinates difference is less than 1 arcmin, that is their formal accuracy: the median difference for the whole set is 3 arcmin and for 14 stars it is larger than 6 arcmin, 2 of them being about 3 degrees off as discussed above.

After having found the actual positions of the Maffei's variables, I looked if they were present in the VSX catalog with another name, adopting a coordinates tolerance of 1 arcmin: these names are reported in  column 8 of Table 1. 

\begin{table}
\small
\caption{Revised coordinates and identifications of variable stars in the field of IC 1805.}
\begin{center}
\begin{tabular}{ccccclrl}
\hline
Maffei&RA1950& DEC1950 &   RAJ2000 & DECJ2000  &   GCVS  &offset  & VSX \\
name  & orig.   &  orig.         &  corrected  & corrected     &   name   &arcmin& ident.\\
\hline
M278&02:41:51&+62:53:00&02:45:31.33&+63:02:19.6&V0690 Cas &4.07& -- \\
M279&02:37:26&+62:31:00&02:24:16.45&+60:27:56.8&V0687 Cas*&186.83& -- \\
M280&02:31:29&+59:45:00&02:35:09.68&+59:55:28.6&V0678 Cas &2.67& -- \\
M281&02:47:50&+59:14:00&02:51:40.21&+59:26:40.8&V0696 Cas*&0.36& Dauban V268 \\
M282&02:43:40&+57:56:00&02:47:29.08&+58:07:32.3&V0692 Cas &1.14& --  \\
M283&02:25:25&+60:17:00&02:28:55.44&+60:23:26.6&V0675 Cas*&7.13& Dauban V264 \\
M284&02:46:57&+58:16:00&02:50:45.86&+58:37:59.4&V0694 Cas*&9.62& Dauban V258 \\
M285&02:17:54&+60:20:00&02:21:12.48&+60:20:11.8&V0725 Cas*&13.78&NSVS 1837975  \\
M286&02:19:42&+59:24:00&02:23:22.56&+59:38:00.9&V0671 Cas &0.42&V0671 Cas  \\
M287&02:27:11&+62:32:00&02:30:27.53&+62:31:45.6&V0647 Cas&14.23&V0647 Cas  \\
M288&02:32:42&+59:10:00&02:36:24.47&+59:21:34.6&V0679 Cas*&1.48&--  \\
M289&02:36:33&+63:14:00&02:56:00.73&+61:24:04.5&V0685 Cas*&169.00&NSVS 1890163  \\
M290&02:24:19&+61:56:00&02:27:34.59&+61:55:57.1&V0674 Cas*&14.08&--  \\
M291&02:56:41&+61:25:00&03:00:39.86&+61:39:50.6&V0699 Cas &2.96&--  \\
M292&02:22:15&+59:24:00&02:25:42.73&+59:31:14.8&V0673 Cas*&6.45&--  \\
M293&02:56:54&+59:31:00&03:00:45.13&+59:43:05.6&V0700 Cas &0.41&V0700 Cas \\
M294&02:32:46&+63:24:00&02:36:06.77&+63:25:11.1&V0680 Cas*&12.70&--  \\
M295&02:33:38&+61:48:00&02:37:09.94&+61:55:22.9&V0726 Cas*&6.16&NSVS 1846691 \\
M296&02:47:05&+61:27:00&02:50:57.00&+61:40:41.9&V0695 Cas &1.46&V0695 Cas  \\
M297&02:35:28&+61:51:00&02:39:04.08&+61:59:16.4&V0684 Cas*&5.11& -- \\
M298&02:35:09&+58:50:00&02:38:55.63&+59:02:08.8&V0682 Cas &0.84&V0682 Cas  \\
M299&02:20:50&+59:11:00&02:24:29.93&+59:24:31.3&V0672 Cas &0.08&V0672 Cas \\
M300&02:50:59&+60:16:00&02:55:02.21&+60:31:09.5&V0697 Cas &3.19&V0697 Cas \\
M301&02:24:01&+60:37:00&02:27:24.01&+60:40:47.7&V0703 Cas*&9.99&NSV 824  \\
M302&02:37:21&+62:22:00&02:40:51.84&+62:29:41.3&V0686 Cas*&6.01& -- \\
M303&02:35:17&+59:31:00&02:39:00.88&+59:42:55.0&V0683 Cas&1.05& NSVS 1925038  \\
M304&02:43:51&+62:30:00&02:47:31.09&+62:41:02.7&V0693 Cas*&2.79&--  \\
M305&02:55:16&+61:02:00&02:59:20.49&+61:18:01.1&V0698 Cas*&4.14&--  \\
M306&02:31:27&+62:59:00&02:34:40.22&+63:00:03.8&V0677 Cas*&13.15&V0943 Cas  \\
M307&02:41:00&+61:52:00&02:44:38.87&+62:02:59.8&V0688 Cas &2.66&NSVS J0244383+620258  \\
M308&02:42:07&+58:10:00&02:45:58.48&+58:22:14.9&V0691 Cas*&0.89&V0691 Cas  \\
M309&02:41:50&+60:26:00&02:45:44.75&+60:39:28.7&V0689 Cas*&0.96&V0689 Cas  \\
M310&02:29:22&+58:12:00&02:33:01.12&+58:25:37.3&V0508 Per &0.44&V0508 Per \\
M311&02:18:29&+60:57:00&02:21:40.87&+60:54:41.6&V0670 Cas*&16.45& DE Cas\\
M312&02:34:51&+58:37:00&02:38:31.49&+58:50:19.1&V0681 Cas*&0.50& V0681 Cas \\
\hline
\end{tabular}
\end{center}
\end{table}


For 11 stars the name in VSX is the same as in SIMBAD: generally this happens because the old coordinates were near to the actual ones. 
For 11 cases a different variable name is listed in VSX, meaning that the variable was `rediscovered' and not recognized as already known because the old coordinates were significantly different from the actual ones: for these stars the two names should be merged in a single identification in variable star catalogues like VSX or GCVS.
For 13 stars no counterpart is present in VSX, indicating that they have not been `rediscovered': for these stars the GCVS variable name can be retained.

To help the reader, and the keepers of variable stars catalogs, I have marked with an asterisk the GCVS star names which, in the last version of the GCVS (Samus et al. 2017), have coordinates different by more than 1 arcsec from my determination and therefore must be updated. 

I remark that the alignment of VSX and CGVS is not always updated to the last version: this is a source of confusion.

\begin{table}
\caption{Table 2. NIR colors, periods and distances for Mira stars.}
\begin{center}
\begin{tabular}{ccrrrrrrr}
\hline  
 Maffei&name&Period&$I-$mean&   $K$     &$I-K$    &$J-H$   &$H-K$  &Dist\\
  ID   & GCVS &days&  mag    &  mag & mag & mag & mag &   kpc   \\
 \hline
M278&V0690 Cas&311&13.85&7.47&6.39&1.12&0.59&8.6\\
M281&V0696 Cas&189.5&13.85&6.95&6.90&1.33&0.73&4.7\\
M282&V0692 Cas&420&14.05&4.86&9.19&1.37&0.80&3.3\\
M283&V0675 Cas&273&12.95&5.93&7.02&1.38&0.75&3.9\\
M284&V0694 Cas&359&14.5&6.90&7.60&1.30&0.83&7.4\\
M285&V0725 Cas&228&14.1&6.57&7.53&1.34&0.69&4.5\\
M287&V0647 Cas&552 & 8.9&3.60&5.30&1.06&0.55&2.2\\
M296&V0695 Cas&166.5&11.1&6.35&4.75&1.03&0.49&3.3\\
\hline
\end{tabular}
\end{center}  
\end{table} 

In Table 2, I report for each Mira star the period in days and the apparent average I magnitude from Gasperoni et al. 1991, the $K$ magnitude, the $I-K$, $J-H$ and $H-K$ colors form 2MASS, and a distance estimate. The distances were computed assuming the absolute $K$ magnitude from the Period-Magnitude relation by Whitelock 2012 ($M_K= -3.69 (\log P-2.38)-7.3$), and a common foreground $K$ absorption of 0.3 mag. These distances are rather indicative because the K magnitude in the 2MASS catalog is taken at an unknown phase in the light curve so may be off up to half magnitude from the average value: a likely error is 0.2 dex in $\log 10$(Dist). Apparently these Mira stars belong to two broad groups, the main one (6 stars) clustered around 3.5 kpc, likely associated to the Perseus arm, while two stars are much farther, around 8 kpc, likely associated to the Outer arm.

There is no clear correlation between the estimated distance of each Mira star and its $J-H$ (or $H-K$) color, so it is unlikely that a different reddening is the main reason for the spread in distances found. 

The $J-H$,$H-K$ color-color plot in Fig. 1 shows the positions of all the Maffei variables with respect to the regions defined by Bessell and Brett (1988). Three groups of stars can be identified in this plot: the first group comprises rather hot stars located on or near the Main Sequence and are generally irregular or eclipse variables; the second group has the Mira and Semiregular variables, with colors typical for this class of stars; the third group has the 4 reddest stars located in the typical area of the carbon stars with dusty envelopes, all classified in Gasperoni et al. (1991) as Semiregular or Irregular: one of them (M280) is already  known as carbon star (CGCS 6035, Alksnis et al. 2001), the others (M 279, M286, M294) are most likely carbon stars too. Also M307 (V688 Cas, CGCS 0396) classified as SR, is a carbon stars, but its colors are not extreme so it is located among the Mira stars in this diagram.

 
\section{Conclusions}
Given that modern catalogs give coordinates more accurate than one arcsec, and that cross-identifications are now based on automatic coordinates matches rather than on visual comparison of finding charts, an update of the coordinates of these variables in the GCVS and VSX catalogs is necessary to allow recovering the variability history of these stars and to allow cross-identifications with present and future galactic plane surveys.

\IBVSfig{10cm}{6236-f1.eps}{The $J-H,H-K$ diagram with the different areas according to Bessel and Brett (1988). Continuous lines are the Main Sequence and the Giant Branch. The star positions are indicatd by letters: M=Miras, S=Semiregulars, I=Irregulars, E=eclipsing stars. The reddening vector is indicated for E($B-V$)=1 mag (A$_K \sim 0.3$ mag). All the stars in our sample fall nicely in this diagram, indicating a small absorption; the carbon stars with dusty envelopes are located in the upper right corner .}
\IBVSfigKey{6236-f1.eps}{}{other}

Thanks to the new more accurate coordinates all these Mira stars can be safely recognized in the forthcoming Gaia catalog of astrometric parallaxes and used to increase the database for studies of the Mira Period-Luminosity relation.


{\bf Acknowledgements:} This work has made use of the SIMBAD, IRSA, VSX and STScI databases.

\references

Alksnis, A., Balklavs, A., Dzervitis, U., et al., 2001, {\it Baltic Astronomy}, {\bf 10}, 1

Bessell, M.S., and Brett, J.M., 1988, {\it PASP}, {\bf 100}, 1134 \DOI{10.1086/132281}

Cutri, R.M., Skrutskie, M.F., vanDyk, S., et al., 2003, {\it CDS on-line catalog}, II/246 \BIBCODE{2003yCat.2246....0C}

Gasperoni, V., Maffei, P., Tosti, G., 1991, {\it IBVS}, {\bf 3573}

Samus, N.N., et al., 2003, {\it Astron. Lett.}, {\bf 29}, 468 \DOI{10.1134/1.1589864}

Samus, N.N., et al., 2017, {\it CDS Vizier catalog}, B/gcvs \BIBCODE{2009yCat....102025S}

Whitelock, P.A.,  2012, {\it Ap\&SS}, {\bf 341}, 123 \DOI{10.1007/s10509-012-0993-x}

\endreferences

\end{document}

