Publications of the Astronomical Society of the Pacific 101: 999-1003, November 1989

RECENT PHOTOMETRIC BEHAVIOR OF THE UNUSUAL Be STAR HD 45677 = FS CANIS MAJORIS

ELAINE M.HALBEDEL* Corralitos Observatory, P.O. Box 16314, Las Cruces, New Mexico 88004 Received 1989 June 15, revised 1989 August 16

ABSTRACT Four years of recent photometry for the unusual Be star HD 45677 = FS CMa is presented. The star is shown to vary actively during the time period observed. A quasi-periodicity of296.5 days has been found for the recent data but does not entirely satisfy historical magnitudes. The feasibility of several models (binarity with a semiregular late-type variable or an infrared object versus motions in the circumstellar shell of a single star) is discussed. A spectrum centered on Ha is presented. Key words: Be star-photometry-circumstellar matter

1. Introduction cool companion is still in the process of formation. Low The star HD 45677 = FS Canis Majoris is an unusual et al. (1970) also suggest a cool companion and that FS member of the class of Be stars. It has been suggested to CMa may be a protostar approaching the main sequence be an object intermediate between a Be star and a plane- and its companion an infrared object like Becklin's object. tary nebula or a symbiotic object. Its spectrum is quite However, another suggestion postulates that the infrared excess is a feature derived from thermal emission from the peculiar, having shown strong Ρ Cygni-type emission at circumstellar dust grains which have a temperature of the Balmer lines of hydrogen and also emission lines of 600 K-1800 Κ (Allen 1971), since there has been no evi- [Fe II], [Ni π], [Cr π], [S ll], and [Ο i]. That it possesses dence of periodicity whatsoever in the radial-velocity an extended thick shell of gas and dust of considerable variations over the past 50 years (Dyck and Milkey 1972). density is inferred from the appearance of the nebular They model the infrared excess by H_ free-free emission lines of [O l] at 6300 and 6363 and of [S ll] at 4068 λλ λ in the metal ionization region. Neither SiO maser radia- (Merrill and Burwell 1933). tion (Dickinson et al. 1978) nor OH emission (Lepine and First noted to have emission at Ha in 1898 (Merrill Rieu 1974) have been detected. In the ultraviolet the 1952), there has never been a time that FS CMa has been spectrum shows an interstellar band at 0.22 μιη and other without hydrogen emission. These line profiles have been lines which suggest high-temperature condensates (Mer- observed to be variable in nature sometimes on the order rill 1979). The infrared spectrum is rich in unidentified of hours (e.g.. Swings (1973) records the disappearance of lines and resembles that of η Carinae and LHa 101 an absorption component of Ηδ in 2 hours). The spectrum (Thackeray and Velasco 1976). Polarization of light has is rich in emission lines both permitted and forbidden. been observed suggesting that the dust grains in the Spectrum variations have been observed in the lines of circumstellar shell are solid dielectric grains with r ~ 0.2 Mg π, He I, and Ca π (Swings et al. 1980). μ (Zellner and Serkowski 1972). The star is not a member FS CMa possesses a strong infrared excess. Indeed, the of a large OB association. infrared produces most of the observed energy flux. Sev- Spectral classification of the underlying star of FS CMa eral models have attempted to account for this by invok- is difficult because of the prevalence of emission lines in ing a cool companion. Ciatti, D'Odorico, and Mammano the spectrum. Previous types have been BQ [ ] (Ciatti (1974) suggest that this companion may be a very late- et al. 1974), BOp (Rufener 1981), B1 (Kilkenny 1978), B2e type giant or supergiant (perhaps representative of the (Merrill 1928), B2q (Allen 1973), B2 IVep sh (Buscombe phase of evolution following long-period variability) or a 1977), B2 IVe (Feinstein et al 1976), B2 IVpe (Kilkenny carbon star. Since there is no radio emission observed and 1981), B3pe (Mendoza 1958), and B3 V (Low et al. 1970). there is an absence of some nebular lines (both of which The estimated υ sin i of 200 km s-1 should be considered would denote a small Η π region), it is possible that the provisional. * Visiting Astronomer, Kitt Peak National Observatory, National Op- 2. The Photometric History of FS CMa tical Astronomy Observatories, operated by the Association of Universi- ties for Research in Astronomy, Inc., under contract with the National Spectroscopy suggests that the extended region sur- Science Foundation. rounding FS CMa is capable of changes on both long and

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© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 1000 ELAINE M. HALBEDEL short time scales. Therefore, it is no surprise that the star B9) and HD 45629 (V - 7.091; {Β-V) = -0.032; B8). is also a photometric variable. Swings and Swings (1972) These magnitudes were derived from all-sky photometry have examined the light curve of this object from the at the Kitt Peak telescope. Only HD 45629 had previ- Harvard plate collection from 1899 to 1963. They found ously published magnitudes: V = 7.10 and (Β—V) = that the amplitude of photometric variation during this —0.04 (Nicolet 1978), in good agreement with the values time has always been less than 0.3 magnitude, with no observed. There was excellent consistency in colors be- trend toward periodicity. Feinstein et al. (1976) have tween the Corralitos and Kitt Peak systems, with there produced the most intensive study of the photometry of being a magnitude difference of0.003 in AV and Δ (ß — V) this star. They found that in 1972 JJBV photometry between the two. This was not considered large enough to showed day-to-day variations of about 0.02 magnitude as correct. The average standard errors in AV and Δ (ß — V) well as large variations of > 0.10 over longer time inter- for the standard stars were found to be 0.025 and 0.024, vals. The star may vary in V as much as 0.5 magnitude respectively. over a year's time, as much as 0.1 in a week or less, and < A total of 47 V and {Β —V) magnitudes were obtained 0.02 in the course of a single night. A variation in V or y is for FS CMa over a time period of JD2446391-7595 (1985 usually accompanied by a change in (B — V), (b—y), or q November 22 to 1989 March 10), or four observing sea- of opposite sign. No periodicities were observed for these sons. Table 1 details the observations while Figure 1 changes. It is suggested that the small brightness in- shows them graphically. It can be seen immediately that creases between 1899 and 1969 proceed from individual FS CMa has been photometrically active during the past mass-loss events, but that the slow and steady decline of four years. The optical brightness has slowly increased in 0.9 V magnitude between 1958-71 may be due to a cloud V magnitude, followed by a decline, with considerable of material passing through the dust cloud region and the scatter. Curiously, counter to the previous behavior line of sight. Walker (1977) used high-speed photometry chronicled by Feinstein et al. (1976), the mean {Β—V) to show that there was no flickering present. does not seem to have changed, though once again there Swings et al. (1980) have examined the correlation of is considerable scatter. A maximum range of 0.431 in V spectrum and photometric changes. They find that the and 0.098 in (β — V) was observed, both within the histor- photometric data and some spectrum features are well ical ranges previously observed. correlated (or anticorrelated) at certain epochs, but that Though previous searches for periodicities in the pho- this trend does not continue. In 1977 they found that tometry of F S CMa have given negative results, it was there was an anticorrelation between H7 and Ηδ absorp- thought useful to perform a periodicity search using the tion cores and U, B,V, and (U~B). At this time He I and discrete Fourier transform method of Deeming (1975) on Mg π also became more intense. When (U—B), {Β —V), the body of data reported herein. The results were some- and V decreased (suggesting that the effect of the dust what unexpected. A range of periods from 0.85 to 601 patches in the shell decreased), the red emission of the days was searched, and two possible periods were indi- Balmer lines increased. However, in 1979 there were few cated: 296.5 and 166.3 days. The first of these was the positive or negative correlations with the spectra, except better of the two in terms of strength of the power spec- that the strengths of the Ca π and M g π absorption lines trum. A third, almost exactly a day, was considered to be were correlated among themselves and with u, υ, {μ—υ), an artifact of the spacing of the observations at a single and C\. observing site. Figure 2 shows this quasi-periodicity plot- There would seem to be some evidence that the in- ted by phase. Of course, it is distinctly possible that other frared colors in the 1.6-3.5 μ region may be variable periods (particularly of short duration) may exist for this (Feinstein et al. 1976). The fourth edition of the General star. After all, the search was done from only 47 data Catalog of Variable Stars states that FS CMa is a *-type points. In the analysis reported on herein all data points variable (denoting uniqueness) which varies from V = were utilized with equal weight, rather than being 7.55-8.58. treated seasonally. Short periods are difficult to deter- mine from collections of magnitudes such as these due to 3. Current Photometry sparse time density. A priori there is no reason to exclude FS CMa has been observed in Β and V magnitudes other periods as being impossible. In addition, Deem- primarily with the 0.6-m telescope and single-channel, ing's method assumes a simple shape for the light curve. photon-counting photometer of the Corralitos Observa- Should it be complex and nonsinusoidal, then further tory. This system utilizes an ambient temperature EMI periods would have been missed. 9924A photomultiplier. Additional magnitudes were also However, with these cautions in mind, this is an inter- obtained with the Kitt Peak Observatory No. 2 0.9-m esting result in view of the previous controversy over telescope and its automated filter photometer with a 1P21 models for the infrared excess of this star. If the magni- photocathode. Comparison stars for differential photome- tude changes are a function of binary motion with the try used were HD 45495 (V = 8.375; {Β —V) = —0.027; supposed infrared companion, then they may have ap-

TABLE 1

Photometry for HD 45677

HJD B-V

6391.9180 8.570 0.072 6429.8614 8.543 0.068 6457.7060 8.439 0.098 6717.9765 8.504 0.088 6734.8917 8.462 0.071 6754.8645 8.426 0.084 6759.9098 8.463 0.075 6773.9257 8.535 0.076 6794.8336 8.377 0.058 6814.7298 8.313 0.025 6828.7634 8.307 0.063 6866.7215 8.25 0.042 6869.6893 8.243 0.042 7066.9595 8.335 0.058 7087.9555 8.299 0.084 7106.9436 8.284 0.073 6400 6600 6800 7000 7200 7400 7600 7124.8682 8.321 0.058 HJD (2440000+) 7127.8468 8.328 0.064 7167.7864 8.139 0.096 Fig. 1-Photometric behavior of FS CMa. 7173.7183 8.257 0.067 7182.8235 8.201 0.050 7185.7755 8.197 0.072 7189.7428 8.230 0.054 7211.6986 8.391 0.077 7230.6661 8.284 0.091 7234.6776 8.338 0.101 7236.6809 8.317 0.060 7255.6316 8.276 0.085 7470.9178 8.309 0.081 7472.8943 8.314 0.066 7474.8840 8.273 0.052 7475.8382 8.274 0.080 Fig. 2-Phase diagram for the quasi-periodicity of 296.5 days. Phases 7477.8654 8.311 0.067 were calculated using an arbitrary Τ0 of JD2446391.9180. 7515.8620 8.240 0.061 7516.7995 8.288 0.064 peared in the observations of the past with the same 7525.8246 8.311 0.062 period. Therefore, some previous photometry was exam- 7526.7656 8.281 0.087 ined with this hypothesis in mind. A similarly long and 7527.8058 8.372 0.034 consistent collection of UBV photometry published by 7540.7627 8.345 0.058 Feinstein et al. (1976) was also subjected to a periodicity 7541.7738 8.409 0.042 search. Several periods were suggested, none of which 7560.6829 8.388 0.051 coincided with that from the recent data. When both data 7561.6585 8.443 0.052 sets were combined and a period search done, two peri- 7590.6499 8.469 0.080 ods besides that near a day were indicated: 283.7 and 7591.6845 8.434 0.104 300.5 days. When examined graphically, the clustering of 7592.6414 8.443 the older data due to fortuitous times of observation 7593.6678 8.451 0.006 makes a conclusion ambiguous. The analysis is dominated 7595.6203 8.268 0.065 by the recent data. However, if binary motion was solely responsible for the quasi-periodic magnitude changes,

© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 1002 ELAINE M. HALBEDEL then collections of previous data such as those repre- sented in Figure 2 of Swings and Swings (1972) would show more irregularity and fewer "standstills" at constant magnitude. Of course, the situation may be complicated by an intrinsic variability of the Β star itself. Nonetheless, at this time it would seem inconclusive that these quasi-periods, if real, have anything to do with binary motion. It is possible that they may represent semistable detached clouds of material rotating about the star in simple orbital motion. Polarization measures by Coyne and Vrba (1976) suggest a model of a dust ring surrounding several gaseous regions in the extended circumstellar disk. They calculate the inner radius of the dust ring to be about 45 AU from the star and its thickness to be 15 AU. Feinstein et al. (1976) also suggest that a model for F S CMa should include a rotating equatorial 6500 6550 6600 6650 lambda (angstroms) ring extending into a dust ring. The quasi-period here discussed would derive from material considerably closer Fig. 3-Spectrum scan of the Ha region of FS CMa. The abscissa is in A to the star than 45 AU and may represent a semistable units, the Ordinate in intensity times the continuum. denser cloud of ejecta from the star. The mechanism for absorption lines. The full width at continuum level of Ha its persistence over such long duration is unclear, how- was found to be 67 A (3061 km s-1), FWHM 5 A (228), its ever, since diffusion of material into what must be a equivalent width 233 A, and maximum intensity 43 X relatively dense and extended cloud would seem to be that of the continuum. He I X6678 is in absorption with a likely in relatively short order. Therefore, the cloud radial velocity of +19.5 km s"1 with respect to the Sun, model as a cause of the semiperiodic photometric varia- not in discordance with the velocity for the entire Ha tion suffers from considerable lack of rigorous physical emission profile of +30.1. X6516 of Fe π is also visible in modeling. double emission and has a velocity of +49.6 km s-1. The If, however, FS CMa is indeed a binary star, then the width for this line at continuum level is 647 km s1. All variability could proceed partially from the secondary star these velocity values are not inconsistent with previously which could be a red semiregular variable of spectral type published values (e.g., Merrill 1952). M, N, or S. The period and amplitude are reasonable for this type of variable, though it is difficult to understand 5. Conclusions why the secondary star is not visible in any region of the FS CMa is by no means representative of the classical spectrum, unless it is heavily veiled by the dust and gas in Be stars in general, but would seem to be more closely the system. It is also possible that if FS CMais apre-main- related to extreme mass-loss stars such as η Car and LHa sequence object, the companion is also a still-contracting, 101. Its relative brightness and extremely variable nature less-massive infrared object. The first of these scenarios is would argue for a profitable spectrophotometric collabo- difficult to reconcile with blackbody models for the in- ration. A definitive conclusion to the binary nature ques- frared excess, all of which have temperatures too low for tion remains unresolved from these data. Photometry has these stars (600 K-1800 K). The second model would been shown here to be a useful tool for plumbing some of most likely produce irregular variability. The situation is the details of the extended shell that surrounds the star. complex. It is difficult to differentiate between these To be most useful, however, simultaneous spectroscopy hypotheses conclusively, although most evidence from should be carried out in the future. The Corralitos Obser- radial velocities, spectra, and infrared analyses would vatory will continue to monitor F S CMa for several ob- seem to point to the single-star hypothesis. serving seasons to come in order to see if the quasi-period 4. A Spectrum of FS CMa persists. Observers who have access to archival photo- trie data are urged to examine them for the periods near A single spectrum of FS CMa in the region centered on 300 days. A sustained series of infrared photometry while Ha was obtained by the author on JD2446875.68113 with the star is varying semiregularly would also be interest- the coudé feed telescope of the Kitt Peak Observatory. ing. This corresponds to near maximum brightness. The spectrum was obtained with an RCA2 CCD. Its resolution was The author would like to gratefully acknowledge 0.89 A per two-pixel linewidth. This spectrum is shown in B. D. Goodrich for assistance with spectrum reduction Figure 3. It reveals an extremely intense Ρ Cygni profile and modifications of the Corralitos photometry system (V/R = 0.6) for Ha as well as several other emission and and also the referee's most helpful comments.

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