A new sample of OH/IR stars in the Galactic center

Transcription

1 ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 128, (1998) FEBRUARY II 1998, PAGE35 A new smple of OH/IR strs in the Glctic center L.O. Sjouwermn 1,2, H.J. vn Lngevelde 3,A.Winnberg 1, nd H.J. Hbing 2 1 Onsl Rymdobservtorium, S Onsl, Sweden 2 Sterrewcht Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlnds 3 Joint Institute for VLBI in Europe, Rdiosterrenwcht Dwingeloo, P.O. Box 2, 7990 AA Dwingeloo, The Netherlnds Received April 14, ccepted June 4, 1997 Abstrct. Two independent, lrgely overlpping 1612 MHz dt sets were serched for OH/IR strs in the Glctic center. One set, tken with the Very Lrge Arry in the period 1988 to 1991, consists of 17 epochs monitoring dt of Vn Lngevelde et l. (1993). The other set ws observed in 1994, using the Austrli Telescope Compct Arry. This rticle describes the dt reduction procedures s well s different wy of serching imge cubes for nrrow line sources, nd lists 1 totl of 155 double pek OH mser detections within 18 or 40 projected prsecs of Sgittrius A*, the compct rdio continuum source in the Glctic nucleus. Presented re 65 formerly unseen double peked 1612 MHz emitters, of which 52 re OH/IR strs. Also given re 3 single pek sources, which we believe to be msers of OH/IR strs. Aprt from being less bright in their 1612 MHz OH mser line, the previously unknown OH/IR strs do not seem to be different from the previously known popultion of OH/IR strs in the Glctic center. We find tht the OH/IR str OH mser luminosity distribution peks t L OH photons per second. Further physicl nd kinemticl nlysis of the new smple will be presented in dditionl ppers. Key words: msers ctlogs surveys strs: AGB nd post-agb Glxy: center rdio lines: strs 1. Introduction When str of low to intermedite min sequence mss (1 7 M ) hs reched the stge where its centrl prt is built up of degenerte nucleus of crbon nd oxygen, Send offprint requests to: L.O. Sjouwermn (Onsl); e-mil: sjouwerm@oso.chlmers.se 1 Tbles 2 nd 3 re lso vilble in electronic form t CDS vi nonymous ftp to cdsrc.u-strsbg.fr ( ), or vi the WWW t Figures 4 nd 5 re only published electroniclly nd obtinble from it strts scending the symptotic gint brnch (AGB) of the Hertzsprung-Russell digrm. While burning hydrogen nd helium in shell round the nucleus it will expnd its envelope. The str pulstes nd strts losing mss t high rte (10 7 to 10 4 M yr 1 ). The str will be obscured in the visible wvelengths by its dense shell of circumstellr mtter. In this slowly expnding nd cooling shell molecules form nd with regulrity conditions re met, such tht the molecules in the circumstellr shell support mser. Since the discovery of the double peked profile of the hydroxyl mser stellite line t 1612 MHz in lte-type infrred strs, the so-clled OH/IR strs hve been studied to investigte stellr evolution nd Glctic dynmics. The chrcteristic double spectrl feture origintes from hydroxyl (OH) msers in the expnding circumstellr shells of oxygen rich AGB strs. It is esy to recognise the object s n OH/IR str; one obtins the position nd line-of-sight velocity of the str s well s the shell expnsion velocity directly from the double peked spectrum. As the vrible stellr rdition t visible nd nerinfrred wvelengths is bsorbed, the only mens of investigting the properties of the underlying str is by observing rdition tht is re-emitted by the shell: infrred nd sub-mm emission of the dust nd gs, in which the molecules cn show mser emission (OH, H 2 O nd SiO). Reviews on the str nd its envelope cn be found in Iben & Renzini (1983) nd in Hbing (1996). Aprt from studying the underlying str, one cn lso mke use of OH/IR strs to probe the Glxy for its structure, evolution nd dynmics. For exmple, Whitelock et l. (1991) derived period-luminosity reltionship similr to the Mir vribles nd Blommert et l. (1994) compred the OH/IR strs in the center, bulge nd outer prt of our Glxy. Good reviews bout using OH/IR strs s tools, re from Hbing (1993) nd Dejonghe (1993). The Glctic center Lindqvist et l. (1992; herefter LWHM) surveyed the Glctic Center (GC) region for OH/IR strs with the

2 36 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Very Lrge Arry (VLA) in 1984 nd The OH/IR strs in the GC re one of the few stellr smples in the GC tht cn be directly observed despite the enormous visul extinction (A V > 25 mg) in front of the GC. The totl of 150 OH/IR strs found (see ppendix) re ll t bout the sme distnce nd thus cn be studied s smple without ssumptions on their individul distnces (e.g. Bud et l. 1981; Jones et l. 1994; Blum et l. 1996). In Lindqvist et l. (1992b) the strs re investigted for their sptil nd kinemtic properties nd used s trcers of the centrl potentil nd mss distribution. It is shown tht the distribution of the GC smple generlly depends on the shell expnsion velocity t 1612 MHz nd tht the surfce density increses strongly towrds Sgittrius A* (Sgr A*). Sevenster et l. (1995) hve shown tht the OH/IR strs in the GC consist of globl Glctic component nd seprte, strongly rotting disk of younger OH/IR strs, possibly formed t distinct event. Unfortuntely the number of OH/IR strs known is too low to do conclusive dynmicl study, especilly within bout pc of Sgr A*. Lindqvist et l. (1997) show tht there should be mny more OH/IR strs in the GC with pprent wek OH msers. The reson why they hve not been found in the LWHM survey is minly mtter of sensitivity. Also the OH msers vry in luminosity, s they re indirectly pumped by the vrible stellr rdition. To find ll strs one should preferbly observe nd serch the sme region for more thn one epoch. By monitoring the vribility of some of the LWHM OH sources with the VLA, Vn Lngevelde et l. (1993; herefter vljghw, or the monitor ) hve tried to mesure phse-lg distnces to these OH/IR strs in order to get direct estimte of the distnce to the GC. However, highly scttering interstellr medium ws discovered in the direction of the GC, mking it impossible to chieve their primry gol (Vn Lngevelde & Dimond 1991). Nevertheless, 20 observtions of the GC region hd been done, ech in sensitivity comprble to the originl LWHM survey observtions. A chep wy of finding fint OH/IR strs is by nlysing the conctented dt set. In tht wy the serch cn be done in highsensitivity dt cube, nd one is ble to detect OH/IR strs which were in minimum of their OH mser luminosity t the time of the LWHM survey. By verging mny different epochs tken over time longer thn the typicl periods of the strs, the detection becomes effectively function of the time verged flux density in the spectrl peks. With 20 epochs, the most sensitive wy to find strs is by using the conctented dt rther thn to serch ll epochs seprtely (under the ssumption tht the OH/IR strs vry typiclly fctor of two during the monitor). We intend to use the new, extended smple of OH/IR strs for testing the loction of, nd probing the potentil in the very center of our Glxy, nd, secondly, to study the smple of OH/IR strs in the GC compred to ll other known smples of OH/IR strs. To overcome symmetry problems, introduced by the prticulr pointing of the VLA dt (optimised for the monitoring progrm; see below), we used the Austrli Telescope Compct Arry (ATCA). The bndwidth for the ATCA observtions hs been chosen to include n equl sensitive serch for high-velocity 2 OH/IR strs (velocity up to 600 km s 1 ), which might dd importnt clues for future dynmicl modelling. Outline of this pper In this pper we describe the dt reduction procedure of the VLA monitor dt set nd of the ATCA observtions in Sect. 2. Section 3 presents list of both known nd suspected OH/IR strs in the GC. Here, when we refer to n OH/IR str, we ctully refer to circumstellr OH mser emission. The lrge interstellr visul extinction prevents us to mke cler distinction between opticlly thick circumstellr shells, s for genuine OH/IR strs, nd opticlly thin circumstellr shells s for the evolutionry closely relted Mir vribles. We my even hve picked up n individul supergint; however, see Blum et l. (1996) for recent evidence tht the number of supergints in the GC is low. Section 3 lso includes n error budget for our mesurements. In Sect. 4, we comment on some of the detections. We discuss the survey sensitivity nd nomlous fetures in some OH/IR str spectr. Briefly, we compre the previously unknown OH/IR strs with the known OH/IR strs nd derive the OH luminosity distribution. From this we conclude in Sect. 5, tht the centrl strs of the new detections re not different from the AGB strs tht constitute the known popultion in the GC. We do not ttempt to mesure the periods of the individul detections s the objects re too fint to be detected in ech epoch seprtely. Also, detiled discussion of the sptil, kinemtic nd physicl properties of the new, extended smple of OH/IR strs in the GC, s well s the issue whether Sgr A* is the dynmicl center of the OH/IR str smple, is deferred to dditionl ppers. A preliminry result on the survey cn be found in Sjouwermn & Vn Lngevelde (1996). 2. Dt hndling nd imge nlysis Tble 1 summrises the chrcteristics of the three different imge cubes mde; Figure 1 depicts n overview of the sky re surveyed, together with the sensitivity contours thereof. 2 Stellr velocities in this pper refer to line-of-sight velocities s mesured with respect to the locl stndrd of rest reference frme (LSR).

3 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 37 Tble MHz survey imge cubes Survey Imge cube center (epoch) Size Resolution Chnnel width RMS Velocity rnge km s 1 khz mjy km s 1 VLA 17 h 42 m 12 ṣ (B1950) b VLA 17 h 42 m 29 ṣ (B1950) c ATCA 17 h 45 m 40 ṣ (J2000) The VLA dt cten The monitor dt ws in 1992 the most extended, uniform 1612 MHz spectrl line dt set of the GC known by the uthors. We did not consider extending the conctention with observtions by others (Hbing et l. 1983; LWHM), becuse those observtions were tken in period when the VLA ws limited in its spectrl line cpbilities. The observtions nd dt reduction of the monitor dt used re described in detil in vljghw. We chose to strt from their clibrted dt sets, minly becuse bd visibilities nd interference from the Russin GLONASS stellite positioning system hd lredy been removed. In summry, the 4 GByte of clibrted visibility dt sets consist of 20 epochs of two-hour VLA observtions, tken in different rry configurtions in the period from Jnury 1988 to Jnury Unfortuntely for the current project, the sky position is not exctly centered on Sgr A*, nd the velocity coverge is limited to only 110 to +190 km s 1. The dt hve been reduced, clibrted nd nlysed using the NRAO AIPS reduction pckge (versions from 15JAN88, up to 15JUL94), which we continued to use on the conctented dt set. Being forced to use different AIPS versions over the yers introduced some problems with the dt tbles during the conctention process. We will comment on tht below. We re confident tht the finl results re not different from wht could hve been obtined if we hd strted with the rw visibility dt nd performed the conctention in one AIPS version only Initil VLA dt set selection The following steps were tken for ech individul dt set to ensure the homogeneity of the sets, before conctenting them to one visibility file for finl processing. Ech of the clibrted monitor dt sets ws checked for consistency by fully imging couple of known strong OH sources. Becuse of different problems, three epochs hd to be regrded lost for our project. We did not process the rw dt, s few missing epochs would not mke significnt difference in the noise sttistics or detection probbilities. Also, due to inconsistent removl of interference in severl epochs, we did not use ny of the visibility dt which could hve been ffected. Therefore, ll dt for which the bselines were shorter thn 3 kλ ws disregrded. If necessry, the u, v, w vectors were reclculted to hve the coordintes (B1950) RA 17 h 42 m 12 ṣ 600 nd DEC s phse center. The lrgest effect of using different AIPS versions could be seen in some tbles contining dditionl informtion to the dt. We minly hd to del with the flgging tbles s the tble formt hd chnged. It ws impossible to restore the originl flgging, so for ech combintion of bseline nd time in flgging tble, ll visibility informtion ws mrked s bd dt. Whenever pplying the tsk SPLIT, the sky frequency (different for ech epoch) nd velocity informtion in ech heder nd ntenn file got reset nd hd to be repired by hnd. As we will not use frequencies (but velocities insted) nd the velocity consistency hd lredy been checked with spectr nd mps, we took n rbitrry file heder nd used it to set ll the relevnt vlues to mtch. The sme ws done for the frequency informtion in the ntenn file. By doing this, one introduces n error less thn 0.05%, in ppernce comprble to rdil bndwidth smering, but in net effect negligible. At this time the dt sets were lso converted from circulr polristions to Stokes I to reduce the file sizes with fctor of two immeditely. As the bsolute flux clibrtion of ech dt set hd been done crefully by vljghw for the flux monitoring progrm, we hve not performed ny further bndpss or mplitude correction, visibility phse reclcultion or flgging opertion on the individul monitor dt sets Conctented VLA dt set processing Alldtsetswereddedinsimilrmnnertocrete one conctented visibility dt set of bout 35 observing hours. Ech epoch ws put in different sub-rry without rescling the visibility weights. Due to different clibrtion pths, the individul weights of the visibility points differed per monitor dt set. To get ech epoch contribute eqully, we treted ll visibility weights to be unity. Although formlly one hs to ccount for the epochs tht re tken in one polristion only (two dt sets before August 1988), we hve not looked into this mtter fter converting ech dt set to Stokes I. To subtrct confusing continuum emission, bseline ws fitted to ech visibility spectrum, using three regions

4 38 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Fig. 1. Composite survey re. The filled circle represents the position of Sgr A*, s well s the center for both the high resolution VLA nd the ATCA imge cubes. The tringle represents the imge cube center for the conctented VLA monitor dt. Long-dshed squres re the 37 VLA nd ATCA surveys; we filtered out the corners for which the distnce to the field (pointing) center ws lrger thn 24. The short-dshed squre encloses the high resolution, 17 VLA imge. Drwn in solid lines re contours of equl detection probbility; lines connecting points with equl sensitivity, ccording to the most sensitive imge cube, fter correcting for the primry bem ttenution (thus cting s primry bem response for this combined survey). Contours drwn re, from inside out, 1.005, 1.1, 1.25, 1.5, 2, 4, 8 nd 16 times 25 mjy. Note tht the VLA bem degrdes fster becuse of lrger dish size; the VLA hs 25 meter, the ATCA hs 22 meter dishes. Approximte J2000 corner coordintes re: upper right 17 h 44 m 05 s to lower left 17 h 47 m 06 s in the totl spectrl bnd which seemed to be void of line sources (Vn Lngevelde & Cotton 1990; Cornwell et l. 1992). Severl chnnels of ech region were verged, nd interpolted to represent the continuum emission. This visibility model for the continuum emission ws subtrcted from ll chnnels of the conctented VLA dt set. On the fly, ll visibility points exceeding twice the expected flux in the chnnel with the strongest source, were clipped. For epoch lignment we used single self-cl itertion on the visibility phses. It corrects for reltive systemtic (tmospheric) effects in the different monitor dt sets. We selected the red shifted pek of OH ; single chnnel with only one strong, 6 Jy pek, nd close to the field center. From this clibrted visibility dt set we mde two nturlly weighted imge cubes nd number of clen boxes ; strong sources outside the min imge cube were mpped in smll fields to limit their side-lobe interference. The first imge cube is full primry bem, low sptil, but full frequency resolution imge cube (survey in Tble 1). The next is smll field, high sptil resolution imge cube ( b ) of the sme VLA dt set, for which we verged two chnnels. The ltter ws centered on Sgr A* nd the not fully removed extended continuum emission of the Sgr A complex. The low resolution imge ws chosen to mtch the sptil resolution of the ATCA. The lrge pixel size resulted in hving only the shorter bselines (bout one hlf of the visibilities) contribute to the imge, wheres for the high resolution imge cube, bout 90% of the visibilities could be used. Using n even higher resolution, to llow ll visibilities to be used, would result in huge mps or lterntively too mny clen boxes (more thn 15). It would thus require n extr pss of subtrction of sources, without substntil decrese in noise level. The numbers used were trde-off between resolution, noise level, sky coverge, execution time nd disk usge. For reference, to mp the entire region t full sptil nd spectrl resolution would require t lest 34 Gb of disk spce (with our choices less thn 4), nd becuse the execution time is strongly dependent on the disk I/O speed, even with modern worksttions it would tke months to execute (compred to hndful of dys). Effectively, only the bselines between 4 nd 32.2 kλ nd 4 nd kλ were used for the low nd high sptil resolution imges, respectively. Fitted RMS noise levels per chnnel were mesured to be 7.2 nd 3.7 mjy on verge, respectively ATCA observtions nd dt reduction The ATCA ws used on 8, 10, 11 nd 13 July To reduce brodbnd interference by GLONASS nd to filter out s much s possible of the extended continuum emission in the GC region, the longest bseline configurtion ws selected for ll the observtions. The GC ws observed t centrl frequency of MHz, covering 8 MHz bndwidth over 1024 frequency chnnels. The integrtion time ws bout 12 hours for ech of the observing dys.

5 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 39 To circumvent GLONASS interference in the bndpss clibrtion, the primry flux clibrtor B ws observed three times per observing run; typiclly every 6 hours. The phse clibrtor B ws observed roughly every 40 minutes. Once per observing run we lso observed the VLA primry flux clibrtor B to check the consistency of the flux density mesurements between the ATCA nd VLA. Actully, for July 10th, we used B for bndpss clibrtion, becuse interference ffected ll B observtions of tht dy. After removing bd visibility dt points nd pplying the bndpss clibrtion, the sky-frequencies were converted to LSR velocities. Following the stndrd phse clibrtion, the extended continuum emission from compct HII regions nd the Sgr A complex ws subtrcted with simple two region bseline interpoltion in the visibility domin. Excessive mplitude visibilities were clipped before pplying one self-clibrtion itertion solution of the visibility phses, on the sme pek nd in similr mnner s to the conctented VLA dt set. Agin we used clen boxes for removing side-lobes of strong sources outside the min imge cube. To void remining effects of interference by GLONASS nd the subtrcted continuum emission of the Sgr A complex in the imge cube, we only used bselines exceeding 4 kλ. Becuse of the lrge mount of disk spce required (5 MB per chnnel), full resolution imges were mde by the hundred for chnnels 69 to 964 ( 600 to 700 km s 1 ). The RMS noise level is bout 4.5 mjy on verge. Becuse we used self-cl to lign different observing dys fter we hd removed ll continuum emission from the dt, ll positions of the OH/IR strs chnged with respect to Sgr A*. Therefore, the chnnel with the mser line we used for self-cl, ws mpped from the unsubtrcted clibrted ATCA dt set. In this mp, the positions of Sgr A* nd the line were mesured, fter which the mser positions with respect to Sgr A* could be determined. The sme ws done for one of the A-rry VLA monitor dt sets. The positionl offsets with respect to Sgr A* in Tble 2 link both VLA nd ATCA observtions together Imge cube nlysis In order to serch for discrete line sources, ech of the three dimensionl imge cubes ws projected into one two dimensionl imge in the following wy: for ech pixel in the sky plne, the mximum intensity over the whole frequency/velocity xis ws stored in new, two dimensionl sky imge. We shll refer to this imge s the mxmp. In tht wy one gets n overll view of the sky loction of intensity mxim, lthough without directly knowing the velocity corresponding to the peks. The mxmp resembles continuum imge (but recll tht we lredy hve filtered out the continuum emission), but with much higher signl to noise rtio thn if we would hve verged the pixel intensities over ll chnnels. Alterntively, one cn mke totl intensity mp (or zeroth order mp ); n imge for which the flux densities tht re higher thn the threshold re integrted over the feture. However, s the totl intensity mp tkes into ccount every pixel bove certin threshold nd thus indeed would be very useful when looking for double peked fetures it is lso very sensitive to brod line sources nywhere in the spectrum. Becuse we hve to del with the remins of the extended continuum emission of the Sgr A complex, we observe vst mount of brod line sources (see lso Fig. 8). These sources cuse severe problems in serching the GC re; from non-liner spectrl slopes to different noise nd detection sttistics. With this in mind, we prefer to use the mxmp insted of the totl intensity mp concept. The finl results in both methods do not differ much, but the serch is much more strightforwrd in the mxmp. Resulting were three mxmps tht ll hve the sme noise level for the detection of sources s the originl imge cubes, but now consisting of pixels contining sources nd the high-end prt of the noise distribution of the originl mp (i.e. only positive vlues round nd bove the RMS noise level; comprble to Ryleigh noise distribution with constnt offset). Now, insted of serching the originl imge cubes in ech chnnel seprtely, nd finding ech source in severl chnnels, one obtins the sme detections by serching the (one chnnel) mxmp only. The mxmps were serched for pixels with intensities over 40 mjy (5.5σ), 25 mjy (6.7σ) nd 25 mjy (5.5σ) for the VLA 37,VLA17 nd the ATCA 37 imge cubes, respectively. Pixels were then grouped in islnds nd for ech islnd, the spectrum in the originl imge cube ws tken t the position with the highest pixel vlue. The mjor dvntge is tht one would only get one spectrum for ech islnd (e.g pixels mke 200 islnds, thus only 200 spectr), risking tht one could miss second object tht is sptilly djcent to the object whose spectrum is drwn. Chnces of missing str re higher close to stronger sources (hving lrger islnds, bem re) nd close to the remnnts of improperly removed continuum fetures of the Sgr A complex (nonliner spectrl slopes). Therefore we checked individul pixels of the locl mxim in the confused re of the centrl 5 by hnd. We think we might hve missed only couple of objects in our totl nlysis. The expecttion vlue for two sources to be positionlly coincident is less thn 1% over the dt set, but on the other hnd we cnnot correct for sources submerged in res of bsorption, or the bowl of negtive emission cused by the extended bckground. The spectr were inspected for second pek, which we required to be t lest 4.5σ (respectively 32.4, 16.6 nd 20.2 mjy observed flux density) nd within the intervl of 5 80 km s 1 of the first pek.

6 40 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Fig. 2. Sky distribution. Closed symbols re new detections, open symbols the previously known OH/IR strs re-detected in this survey. The offsets refer to Sgr A* ( l, b in Tble 2). Note tht the overll concentrtion of the new detections towrd the center is prtly due to the survey bem response (Fig. 1); the concentrtion in the very center is however rel 3. Results Figures 2 nd 3 summrise our results, where it should be noted tht the stronger (previously known) sources cn be detected further out from the pointing center becuse of the drop in sensitivity. Tbles 2 nd 3 (lso vilble electroniclly through CDS) list ll detections within the surveyed re, lso when it concerns previously known source. Figures 4 nd 5 (only vilble electroniclly through CDS) disply the 1612 MHz OH mser spectr of ll sources. Single pek or suspected double pek detections with pek flux exceeding 8σ (36 mjy before correction in the ATCA dt), re lso listed. However, we do not list ny of the obvious single peks in the region where confusion with the extended continuum emission occurs. These detections re probbly not of stellr origin. This mens we hve excluded ll single pek detections within the box defined by lɛ[359.92, ], bɛ[ 0.08, 0.03], even when the pek flux exceeds 36 mjy. Actully, some of the double pek detections in this region might be debtble for being stellr sources. Such cses re indicted in Tble 3. In cse of filure detecting the second pek, we usully took the velocity of the second pek from our VLA/ATCA dt, or else from LWHM. For ech detection, t the red nd blue shifted peks, fluxes nd velocities were determined. The position, together with the forml errors were mesured with the Fig. 3. Velocity distribution. Symbols s in Fig. 2. The dotted lines outline the limited coverge of the monitor; the solid lines the velocity intervl covered by LWHM AIPS fitting progrm IMFIT, in the chnnel with the highest pek flux. For the VLA dt, J2000 positions nd Glctic coordintes (l, b) were clculted from the B1950 positions nd then truncted ccording to the IAU convention. The Glctic coordintes from the ATCA dt were clculted fter the inverse trnsformtion from J2000 to B1950. All positionl nd kinemtic dt of the detections re given in Tble 2. Tble 3 lists corresponding physicl dt to ech entry in Tble 2. Where pproprite, we first list the VLA (, or b ) nd secondly the ATCA ( c ) dt. If seen in both the low nd high resolution VLA imge cubes, we used the high resolution ( b ) result for the position (Tble 2) nd the low resolution ( ) result for the velocity nd flux informtion (Tbles 2 nd 3 nd Fig. 4); the other result ws used s consistency check in such cses. As the fluxes mesured for the VLA dt re verges over 17 observtions nd depend on the resolution, we show VLA nd ATCA spectr seprtely in Fig. 4 nd in Fig. 5. There re considerble difficulties when reching such low noise levels in the GC re; residuls of the extended OH bsorption, continuum subtrction, nd very strong mser sources cuse poor bselines in both the VLA nd ATCA dt. Therefore, t the position of the str in the imge cube nd voiding the region of the stellr mser emission, liner bseline ws fitted to, nd subtrcted from the spectrum.

7 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 41 Tble 2. OH/IR strs in the Glctic center: positionl nd kinemtic dt OH Nme R. A. nd Declintion δ mx V blue V red V str l b Ref. J km s 1 km s 1 km s 1 c (13) c (14) c (17) c (18) c (19) (21) c (21) c (22) (23) c (23) c (24) (25) c (25) (26) c (26) c (27) c (29) (31) c (31) c (32) c (32) (33) c (33) (34) c (34) (35) c (35) c (36)

8 42 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Tble 2. continued OH Nme R.A. nd Declintion δ mx V blue V red V str l b Ref. J km s 1 km s 1 km s (37) c (37) b (38) c (38) c b * (40) c (40) c (41) b (42) c (42) c (43) (5) c (5) b (44) c (44) (45) c (45) b (47) c (47) (46) c (46) b c c b (48) c (48) b (6), 6 c (6), 6 b (50) c (50) c c

9 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 43 Tble 2. continued OH Nme R.A. nd Declintion δ mx V blue V red V str l b Ref. J km s 1 km s 1 km s 1 b b c b c (51) c (51) b b (52) c (52) b (53) c (53) (55) c (55) (56) c (56) b c c (57) c (58) b , * c , * b (59) c (59) c c b (60) c (60) c c b (61) c (61)

10 44 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Tble 2. continued OH Nme R.A. nd Declintion δ mx V blue V red V str l b Ref. J km s 1 km s 1 km s 1 c b b (7) b c b (62) c (62) b (63) c (63) c * c * c (64) b c c b b (65) c (65) c b * b b (66) c (66) c b (67) c (67) b (68) c (68)

11 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 45 Tble 2. continued OH Nme R.A. nd Declintion δ mx V blue V red V str l b Ref. J km s 1 km s 1 km s 1 b c c c b b c c b * b (69), * b c b (70) c (70) b (8) c (8) (71) c (71) c b (72) c (72) b c b (73) c (73) b * c * b * c * b (74) c (74)

12 46 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Tble 2. continued OH Nme R.A. nd Declintion δ mx V blue V red V str l b Ref. J km s 1 km s 1 km s 1 b c b (75) c (75) (76) b (77) c (77) b * c * c b c (78) c (78) (79) c (79) b c b ? c ? (80) c (80) b c b (81) c (81) b c b c

13 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 47 Tble 2. continued OH Nme R.A. nd Declintion δ mx V blue V red V str l b Ref. J km s 1 km s 1 km s c b (82) c (82) b (83) c (83) c * b c (84) c (84) (85) c (85) b (86) c (86) b (87) c (87) (88) c (88) c b (90) c (90) c c (92) c (92) (91) c (91)

14 48 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Tble 2. continued OH Nme R.A. nd Declintion δ mx V blue V red V str l b Ref. J km s 1 km s 1 km s (93) c (93) (94) c (94) (95) c (95) (96) (97) c (97) (98) c (98) (99) c (99) (100) c (100) (101) c (103) (105) c (105) c (106) c (107) c (108) c (111) c (111) c (112) c Lindqvist et l. (1992) (number) nd references therein 4 Levine et l. (1995) 1 Lindqvist et l. (1992), single pek (number) 5 Yusef-Zdeh & Mehringer (1995) 2 Bud et l. (1975) 6 I.S. Glss, pers. comm. (Glss et l. 1996) 3 Vn Lngevelde et l. (1992) * See remrks in min text.

15 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 49 Tble 3. OH/IR strs in the Glctic center: physicl dt OH Nme PBF S blue I blue ɛ S red I red ɛ V exp L OH Deconvolved Note 1 b mjy % mjy % km s c c c c LWHM c c c ATCA c c c c c LWHM c c c c c c c c

16 50 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Tble 3. continued OH Nme PBF S blue I blue ɛ S red I red ɛ V exp L OH Deconvolved Note 1 b mjy % mjy % km s c c c c c c c LWHM c c c c c ATCA c c c c c c c

17 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 51 Tble 3. continued OH Nme PBF S blue I blue ɛ S red I red ɛ V exp L OH Deconvolved Note 1 b mjy % mjy % km s c c c b c c c c ATCA c c c c ATCA c c c ATCA c c MC? c MC ATCA c

18 52 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Tble 3. continued OH Nme PBF S blue I blue ɛ S red I red ɛ V exp L OH Deconvolved Note 1 b mjy % mjy % km s c MC b ATCA c ATCA c c c MC? c MC? c MC c MC c b MC c c b c c MC? c c

19 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center 53 Tble 3. continued OH Nme PBF S blue I blue ɛ S red I red ɛ V exp L OH Deconvolved Note 1 b mjy % mjy % km s c c c MC b MC c MC c MC b MC c MC c c MC c MC c MC c c c c c c

20 54 L.O. Sjouwermn et l.: A new smple of OH/IR strs in the Glctic center Tble 3. continued OH Nme PBF S blue I blue ɛ S red I red ɛ V exp L OH Deconvolved Note 1 b mjy % mjy % km s c c c c VLA c c c c ATCA c VLA c c c c b c b c