The Missing Symbiotic Stars: A Joint Analysis with Gaia, GALEX, and XMM-Newton Data

The existence of a population of low-accretion-rate symbiotic stars (SySts), consisting of a giant star and a compact companion (usually a white dwarf), has been proposed recently. However, their population has not been fully understood. In this work, we present an investigation on SySts candidates consisting of asymptotic giant branch stars (AGBs) by cross-correlating the Gaia DR3, the Galaxy Evolution Explorer All-Sky Imaging Survey, and the 4XMM DR13 catalogs. We first build a sample of AGBs within 500 pc based on their locations in the Gaia color–absolute magnitude diagram. We then explore the UV and X-ray properties of the sampled AGBs and compare them to known SySts and candidates. We find 10 SySts candidates based on the far-ultraviolet excess. The typical UV luminosity of the candidates is 1031 erg s−1, which corresponds to a typical accretion rate of 10−12–10−11 M ⊙ yr−1, which is more than 1 order of magnitude lower than known SySts. Based on these findings, the total number of SySts within 500 pc is estimated to be 18. The number of AGBs with X-ray flux above 10−14 erg s−1 cm−2 within 500 pc is estimated to be 37. Our finding implies that a large number of low-accretion-rate SySts are yet to be detected, which provides a base for a complete understanding of their population.


Introduction
Symbiotic stars (SySts) are a class of binary stars where a white dwarf (WD) accretes matter from its red giant companion via Roche-lobe overflow or/and the stellar wind. 1 The accreted matter is then heated and emits X-ray and ultraviolet (UV) photons.SySts are natural laboratories to test the stellar evolution theory and are closely related to important astrophysical objects like the progenitors of Type Ia supernovae (SNIae; e.g., Mukai 2017;Liu et al. 2019).
The population and evolution of SySts have not been fully understood.Although the most recent catalog of SySts includes 410 sources (Akras et al. 2019a), the number of SySts in the Milky Way remains highly uncertain, with estimated numbers ranging from 10 3 to several 10 5 (Kenyon 1986;Magrini et al. 2003;Lü et al. 2006;Mikołajewska 2012;Mukai et al. 2016;Mukai 2017;Munari 2019).It is also not clear how the wind mass-loss rate of a giant star would be affected by the presence of a WD companion (Tout & Eggleton 1988;Meng & Han 2016), how the disk thermal-viscous instability works (Hameury 2020), and what the emission mechanism of lowaccretion-rate WDs is.To improve our understanding of the above issues, it is crucial to set up a representative sample of SySts.
An SySt is usually identified from its optical spectrum: a star showing both the spectrum of a molecular absorption band component, e.g., the TiO bands, and prominent high-excitation emission lines (e.g., Li et al. 2015;Akras et al. 2019a;Jia et al. 2023).However, recent investigations on SU Lyn suggested that a giant star exhibiting no significant emission lines could also be a genuine SySt (Mukai et al. 2016;Munari et al. 2021;Iłkiewicz et al. 2022).The absence of the emission lines was proposed to be due to the low accretion rate, so that stable H burning on the WD surface and the ionization of the stellar wind of the cool giant are both suppressed.Based on their findings, Mukai et al. (2016) suggested that a significant population of SySts with low accretion rates might have been missed in previous low-resolution-spectroscopy surveys.This proposal motivated a series of papers dedicated to the search for low-accretion-rate SySts.Recent works include the finding of 33 candidates using the GALAH high-resolution spectroscopic survey of the Southern hemisphere (Munari et al. 2021), and the identification of THA 1531 as an accretion-only SySt (Munari et al. 2022).However, it is still not clear how many such systems exist in the solar neighborhood, which is the main motivation of this work.
The far-ultraviolet (FUV) excess of asymptotic giant branch (AGB) stars was proposed as the indicator of the presence of either a hot WD companion or an accretion disk, and therefore a criterion for SySts (e.g., Sahai et al. 2015Sahai et al. , 2018;;Montez et al. 2017;Akras 2023).AGBs are medium-mass (∼1-8M e ) stars in their late evolutionary stage.The helium supply in their cores is exhausted so that the helium burning only continues in the inner shells.Various studies have been done to explore the properties of AGBs and their relation to SySts (e.g., Whitelock et al. 2008;Gromadzki et al. 2009;Akras et al. 2019b).The most recent work by Akras (2023) demonstrated a valuable method to search for SySts in giant stars with FUV excess.They started from existing variable star catalogs, and stars fulfilling the IR (Two Micron All Sky Survey (2MASS)/ AllWISE) criteria of S-type SySts were selected to ensure the presence of a red giant companion.Then, the sampled stars were cross-matched with the Galaxy Evolution Explorer (GALEX) All-Sky Imaging Survey (AIS) catalog, and those with m FUV − m NUV <1 were selected as SySt candidates.In this way, tens of SySts candidates were discovered, and two (40%) were identified to be genuine SySts in the following spectroscopic observations on five sources (Akras 2023).These findings provide a new probe to search for SySts within current star catalogs.However, the existing star catalogs (e.g., Suh 2021;Iwanek et al. 2022;Li et al. 2022) are constructed with data from different instruments and are usually fluxlimited.As a result, the proposed SySts and candidates could be strongly biased.
The release of Gaia DR3 parallax measurements on nearby stars allows an improved investigation on SySts in a volumelimited way (Gaia Collaboration et al. 2016;Gaia Collaboration et al. 2023).In this work, we limit our research on AGBs to reduce contaminations from various classes of sources (e.g., active galactic nuclei (AGNs), young stellar objects, etc.) We start by defining a volume-limited sample of AGBs within 500 pc of their location in the Gaia DR3 color-absolute magnitude diagram (CaMD).We then cross-correlate this sample with GALEX AIS and XMM-Newton catalogs to examine their UV and X-ray properties.We finally select SySts candidates based on their m FUV − m NUV color, and estimate the number of SySts within 500 pc.
The rest of the paper is organized as follows.In Section 2, we present our search methodology.In Section 3, we present the UV and X-ray properties of the sampled sources and a catalog of SySt candidates within 500 pc.We briefly discuss the implications in Section 4 and summarize our results in Section 5.

Preselection of AGBs
Our goal in this work is to find SySts and their candidates in a certain volume for statistical investigation.We started by selecting AGBs from the Gaia DR3 CaMD.To reduce false match probability and foreground absorption, we limit our targets to stars within 500 pc by implementing selection criteria: PARALLAX 2.0 to Gaia DR3 sources and find ∼6 × 10 7 sources within 500 pc (the G500 sample hereafter).
We then cross-correlate the carbon-rich AGB-IRAS and oxygen-rich AGB-IRAS catalogs by Suh (2021)2 with the G500 sample and find 133 matches (the AGB500 sample hereafter), as plotted in Figure 1.Obviously, the majority of matches in the AGB catalogs are located in a certain region in the Gaia CaMD, which fulfills the criteria set by Akras (2023) (M G < 5.0 and B P − R P > 2, where M G and B P − R P are Gaia G-band absolute magnitude and B p − R p color, respectively).We then manually define a region in the CaMD diagram BP_RP>1.86 M_G < = 5.0 M_G<2.27273* BP_RP-5.82.The region is defined to make a balance between the source reliability and the number of available sources (121 out of 133, or ∼90% of stars in the AGB500 sample are located in this region).We find 2238 sources in Gaia DR3 pass the above selection (the G500AGB sample),3 shown as magenta dots in Figure 1.
To verify the selection criteria of the G500AGB sample, the sampled stars are cross-correlated with the 2MASS catalog (Skrutskie et al. 2006), and plotted in the J − H versus H − K s color-color diagram in Figure 2. We find 76% of the G500AGBs are nicely located in the region of the S-and D-type SySts (e.g., Phillips 2007;Corradi et al. 2008;Baella et al. 2016;Akras et al. 2019b;Akras 2023), and the contamination sources are likely giants according to their location in this plot (Akras et al. 2019b) and in the Gaia CaMD (Figure 1).We further plot the 10 candidate SySts selected by their UV color (see Section 3.2 for details); nine of them are  located in the S-and D-type SySt region and the other one is fairly close to the left boundary of the region.We further plot the known SySts in Figure 1, and find that ∼50% of them are located within the defined G500AGB region.

The UV Source Catalog
We use the GALEX GR6/7 AIS source catalog (Bianchi 2009) in this work.As described in Bianchi (2009), Bianchi et al. (2017), and Figure 1.1 in the GALEX data description webpage,4 the AIS covers about two-thirds of the sky with a typical exposure of ∼100 s, corresponding to a detection limit of ∼20 (∼21) magnitude in the FUV (near-ultraviolet (NUV)) band.The respective limit FUV and NUV luminosities for a source located in a distance of 500 pc is thus in the order of 10 30 erg s −1 (see Section 4 for details), which is also the limit of our UV cross-correlated sources.

Preselection of XMM-Newton Sources
We inspect the 4XMM DR13 catalog (Webb et al. 2020) in this work.Compared to earlier surveys, XMM-Newton observations are substantially more sensitive.The catalog is constructed from 13,243 XMM-Newton/EPIC observations, covering 3.2% of the sky, which is considerably greater than similar modern X-ray source catalogs.The catalog contains a total of 983,948 detections.We first exclude 284,972 sources with SUM_FLAG > 1 (clean detection) to minimize the probability for spurious detections,5 which leads to a total of 6.9 × 10 5 sources.We further apply a 0. We adopt F c = 2.0 × 10 −14 erg s −1 cm −2 , because it is the detection limit for a 7 ks XMM-Newton exposure at the 15′ off-axis angle;6 ∼86% of XMM-Newton observations used in the catalog have deeper exposures. 7This F c is equivalent to an X-ray luminosity of L c ∼ 6.0 × 10 29 erg s −1 at 500 pc, which is about 2 orders of magnitude lower than most known SySts (Luna et al. 2013) and 1 order of magnitude lower than the accretion-only SySt SU Lyn in its quiescence (Mukai et al. 2016;Iłkiewicz et al. 2022).This selection leaves 3.5 × 10 5 4XMM sources (the 4X catalog hereafter) for further correlating.

The Cross-correlating
The G500AGB sample is cross-correlated with the GALEX GR6/7 AIS catalog to search for the UV counterparts of AGBs.The crossing makes use of the software TOPCAT (Taylor 2005) with a 6″ matching radius considering the GALEX PSF in the FUV and NUV bands (Morrissey et al. 2005;Ortiz & Guerrero 2021).As shown in Figure 3, the choice of the exact value of matching radius (e.g., 5″ in Akras 2023) does not affect the final sample of candidates.The cross-correlation results in 1177 total matches (the G500AGB_UV sample hereafter), 890 of which are detected in both FUV and NUV, and 10 of which show m FUV − m NUV <1.Only one G500AGB source (0.08%) is found to have more than one GALEX match and is negligible in the following statistical analysis.The offset distribution for the matches is rather small (97% of them are less than 2 0), as plotted in Figure 3.
The G500AGB sample is further cross-correlated with the 4X catalog to search for the X-ray counterparts.The crossing radius is set to 5″, which accounts for much of the position uncertainties (e.g., Xu et al. 2022).The cross-correlation finds six total matches (the G500AGB_X sample hereafter), all of which are single matches with matching radii below 1″.
For comparison, we cross-correlate the SySt catalog by Akras et al. (2019a) with the GALEX catalog, and find 37 matches with positive Gaia parallax values (the SySt_UV sample hereafter, see the supplementary table for details), 34 of which have both FUV and NUV detection.We further find 47 sources in the SySt_UV sample have Gaia DR3 counterparts, and five of them are within 500 pc.We also cross-correlate the SySt catalog with the 4X catalog and find 25 matches.
We cross-correlate the 10 G500AGB_UV sources with m FUV − m NUV <1 with Lamost DR11 and Sloan Digital Sky Survey DR16 databases and none of them are found to have optical spectra.The low-resolution Gaia DR3 XP spectra, although available, could not constrain the presence of weak emission lines that are found in low-accretion-rate SySts (Mukai et al. 2016), and are therefore not discussed in this work.

Results
We present the properties of known SySts and identify new SySts candidates based on such properties in this section.

The Spatial Distribution of UV Counterparts
Figure 4 presents the spatial distribution of the G500AGB and the G500AGB_UV stars.As shown in the Figure, the G500AGB stars seem to be randomly distributed in the sky.A Kolmogorov-Smirnov test is performed to check the effect of scale heights of AGBs on the distribution of the stars within 150 pc and those between 150 and 500 pc as a function of the absolute Galactic latitude.However, there is no significant difference between the two distributions, we therefore conclude that the vertical scale height of the AGB stars can not be constrained by the current sample.

The UV Counterparts
In Figure 4, the spatial distribution of the G500AGB_UV stars is also plotted.Naturally, the G500AGB_UV sample lacks stars with low Galactic latitudes, since GALEX AIS avoided observing near the Galactic plane. 8For the same reason, we do not consider the foreground absorption in this work, since they are expected to be small in directions other than the Galactic plane in a 500 pc radius volume.
The left panel of Figure 5 compares the distribution of the FUV and NUV magnitudes of the G500AGB_UV stars and those of the SySts_UV sample.The NUV magnitudes of both samples cover a wide range from 12 to 23 mag.However, the G500AGB_UV stars tend to be much fainter in the FUV band (with a median value of 21.2 mag) than the SySts_UV sample (with a median value of 16.6 mag).As shown in the figure, 35 (73%) of SySts_UV stars with both FUV and NUV detection show FUV − NUV < 1, while only 10 out of 890 (1.1%) G500AGB_UV stars exhibit a similar FUV excess.This FUV excess (FUV − NUV < 1), as discussed by Akras (2023), is most likely due to the strong FUV emission associated with the accretion of matters onto the WD in SySts, and thus could be employed as a key criterion to separate SySts from normal AGBs.
We apply the FUV − NUV < 1 criteria (Akras 2023) to the G500AGB_UV sample, and find 10 SySts candidates, whose properties are listed in Table 1.Their classification in SIMBAD includes long-period variables, Miras, or AGBs.We plot the 10 candidates in the left panel of Figure 5

X-Ray Counterparts
In Table 2, we present the properties of the six G500AGB_X sources, two of which (V1261 Ori and CH Cyg) are identified SySts, and the other four are classified as Miras or long-period variables in Simbad.Among the six G500AGB_X sources, five had XMM-Newton on-axis observations, and their X-ray properties have been investigated in previous work (Ortiz & Guerrero 2021;Lima et al. 2023;Toalá et al. 2023).CK Phe, on the other hand, was observed serendipitously and its limited counts do not allow a spectroscopic analysis.We therefore define a 2-12 keV to 1-2 keV hardness ratio (HR): (PN_5_RATE + PN_4_RATE − PN_3_RATE)/ (PN_5_RATE + PN_4_RATE + PN_3_RATE) to represent the hardness of their X-ray spectra, where PN_5_RATE, PN_4_RATE, and PN_3_RATE are the XMM-Newton/EPIC PN count rates in the 4.5-12 keV, 2-4.5 keV, and 1-2 keV bands (Webb et al. 2020).
Figure 6 compares the HR distribution of our counterparts and that of the known SySts.In the figure, SySts are naturally divided into two groups by a critical HR of ∼ − 0.3: the "soft" group consisting α and β types of SySts where H burning or wind-collision takes place (the two "soft" group sources with HR = 1 is due to the absence of photons in 1-2 keV), and the "hard" one including the δ and β-δ types where hard X-ray emission powered by the boundary layer was found (Luna et al. 2013).Obviously, four out of six candidates (including the two identified SySts: V1261 Ori and CH Cyg) nicely fit into the "hard" group, judged by their HR values.The X-ray luminosities of the candidates cover a range from several 10 28 erg s −1 to 10 32 erg s −1 , which is comparable to or lower than the known SySts.

Discussion
Here we briefly discuss the implications of our results.

EY Hya
EY Hya is the only sampled source that has been detected both in X-ray and UV bands.It was investigated by Ortiz & Guerrero (2021) and a mixture of βand δ-type emission was found.As shown in Table 2, its X-ray luminosity (1.3 × 10 31 erg s −1 ) and HR (∼ −0.27) are comparable to accretion-only SySts like SU Lyn.
The X-ray properties of EY Hya are similar to low-accretionrate SySts.As shown in Figure 7, a refitting of its X-ray spectrum (which was downloaded from the 4XMM catalog website) with an optically thin, multi-temperature plasma model (mkcflow in xspec) reveals a maximum temperature of 12.4 1.6

-+
keV with a reduced chi-square value of 0.96/39.This temperature is consistent with what would be expected from a 0.8M e accreting nonmagnetic WD (Yu et al. 2018) and is way higher than what is expected for accretion onto a mainsequence companion (∼1 keV; see Yu et al. 2022).

Number of SySts in 500 pc
The finding of 10 SySts candidates covered by GALEX within the AGB region within 500 pc, if confirmed, may suggest that a large number of SySts are still missing within the 500 pc radius volume.To make a reasonable estimation of the genuine SySts within 500 pc, we need to account for the SySts AIS coverage (60%) and the SySts fraction in the UV-selected candidates (40%; Akras 2023).We also need to take into account the SySts that are not located in the defined AGB region (50%; see Figure 1) and SySts that have UV counterparts but do not pass the m FUV − m NUV cut (27%).9Therefore, the number of missing SySts within 500 pc is 10/60% * 40%/ 50%/73% = 18, which is more than 3 times the number of known SySts within 500 pc (five).The missing SySts may be accretion-only sources whose accretion rates are too low to produce emission lines, and therefore might be missed in previous surveys, as suggested by Mukai et al. (2016), Iłkiewicz et al. (2022), andAkras (2023).Their typical FUV+NUV luminosity is roughly estimated as 10 30-31 erg s −1 , by using the magnitude-to-flux conversion factor from Bianchi (2009).Of course, the real UV luminosity may be several times higher considering the limited energy coverage of the GALEX detections, but the difference would not affect the qualitative analysis.Assuming the UV emission originated from the WD accretion, and taking the typical luminosity ratio L UV /L X ∼ 10 (Luna et al. 2013), we can estimate a typical accretion rate of ∼10 −12 -10 −11 M e yr −1 for a 0.8M e WD.Such low mass accretion rates may occur in wideorbit (P orb > 10 4 days) SySts (e.g., Yu et al. 2022), whose existence have been predicted by population synthesis works but were rarely confirmed observationally (Mikołajewska 2012).These SySts would be natural laboratories to investigate the stellar evolution and accretion theories, e.g., the wind mass-loss rate, the disk thermal-viscous instability (Hameury 2020), and the emission mechanism of lowaccretion-rate WDs.We strongly encourage further X-ray, UV, and optical observations on these candidates to clarify their nature.

X-Ray-emitting AGBs
It would be premature to make any justifications on the nature of the other three unclassified G500AGB_X sources based on the limited information provided by X-ray observations only.Here we instead try to make an estimate of the number of X-ray-emitting AGBs present within 500 pc from the Sun.X-ray-emitting AGBs have been intensively studied in recent years and were proposed to include various classes of sources: SySts, AGBs with a dwarf star as companions, etc. (Sahai et al. 2015(Sahai et al. , 2018;;Ortiz & Guerrero 2021).The estimate is made by using a method similar to that in Xu et al. (2022), which involves the treatment of 4XMM sky coverage (3.2%) and the exposure coverage (85% above 7 ks).Among the 6 G500AGB_X sources, only one of them (CK Phe) was observed serendipitously.Therefore, there would be 1/3.2%/85% = 37 AGBs with X-ray flux in the order of 10 −14 -10 −13 erg s −1 cm −2 within 500 pc, which are too faint to be detected in previous all-sky X-ray surveys.Compared with the estimated number of SySts (18) within 500 pc, the probability of an X-ray-emitting AGB being a SySt would be ∼50%.With the forthcoming eROSITA data release, we expect to find more X-ray-emitting AGBs and to better understand their nature.

Summary
In this work, we search for SySts candidates within 500 pc by cross-correlating Gaia, GALEX, and XMM-Newton catalogs, and put constraints on the number of SySts in this volume.
We find 10 SySts candidates with typical UV luminosity of 10 30-31 erg s −1 within 500 pc based on their m FUV − m NUV color.The total number of SySts in this volume is estimated to be 18, more than 3 times the number of known SySts.This finding implies that there would be a hidden population of SySts whose accretion rates are more than 1 order of magnitude lower than known SySts.We also find six X-ray counterparts to the sampled AGBs, and estimate the number of AGBs with X-ray flux above ∼10 −14 erg s −1 cm −2 within 500 pc to be 37.One of the AGBs (EY Hya) has been observed by both XMM-Newton and GALEX and is proposed to be a good candidate of accretion-only SySts based on its X-ray and UV properties.
We strongly encourage further spectroscopic observations to testify to the nature of the SySt candidates and to put constraints on the number of SySts in the Galaxy.The forthcoming data release of eROSITA would also be very useful to explore the population of SySts.
National Key R&D Program of China (grant No. 2023YFA1607902) and the Natural Science Foundation of China under grant No. 12373034 and by the China Manned Space Project of No. CMS-CSST-2021-A10.This work has made use of data obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.This work has made use of data obtained from the 4XMM XMM-Newton serendipitous source catalog compiled by the XMM-Newton Survey Science Centre consortium.This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia),processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular, the institutions participating in the Gaia Multilateral Agreement.This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.We acknowledge the use of the GALEX public archive.We also acknowledge the use of the SIMBAD database, operated at CDS, Strasbourg, France.

Figure 1 .
Figure 1.B P − R P color-absolute G-band magnitude diagram of Gaia stars within 500 pc (G500, gray), also shown are known AGBs within 500 pc (red) and known SySts (blue).Our sampled sources (the G500AGB sample) are shown to be enclosed within a magenta-colored region.The thick magenta line indicates the M_G<2.27273* BP_RP-5.82 as one of our criteria for selecting the AGB sample.

Figure 2 .
Figure 2. The J − H vs. H − K s color-color diagram of the G500AGB sample (gray) and the 10 candidate SySts (red) in Table 1 selected by UV color (see the main text for details).The solid and dashed boxes indicate the region of S-and D-type SySts region defined in Akras et al. (2019b) and Akras (2023).

Figure 3 .
Figure 3.The distribution of matched radii of G500AGB_UV sources.
to compare with SySts and the Akras (2023) candidates.From the figure, the three samples share an NUV magnitude range from 14 to 20 and an FUV magnitude range from 14 to 21.However, the Akras (2023) sample contains additional faint sources with 20 < m NUV < 23 and 21 < m FUV < 22, which is likely due to the inclusion of distant sources in their sample.We further compare the absolute UV magnitudes of the three samples in the right panel of Figure 5.As shown in the figure, the median absolute UV magnitudes of the 10 candidates are M FUV = 10 and M NUV = 9.4, which are 2 to 3 magnitudes fainter than those of the Akras (2023) sample (M FUV = 7 and M NUV = 6.4) and 3 to 4 magnitudes fainter than those of known accretiononly SySts (M FUV ∼ 6.4 and M NUV ∼ 5.4) or SU Lyn (M FUV ∼ 7.1 and M NUV ∼ 6.7).In other words, we are detecting giant stars whose UV luminosities are ∼10% of those in Akras (2023) and ∼5% of known accreting-only SySts.

Figure 4 .
Figure 4. Spatial distribution of G500AGB (gray), G500AGB_UV (red), and the 10 SySts candidates (green) in the sky projected in the Galactic coordinates.

Figure 5 .
Figure 5. Left: the FUV and NUV magnitude distribution of the G500AGB_UV (gray dots), the SySts_UV (blue dots) samples, and the SySt candidates by (Akras 2023; magenta dots); the 10 G500AGB_UV SySt candidates (green circles) and SU Lyn (the red cross) are also plotted for comparison.Right: the absolute FUV and absolute NUV magnitudes of the samples.
Notes.aThe only candidate with both X-ray and UV observations.b Sources classified as SySts in Simbad.Columns are simbadID, name as listed in Simbad; R.A. and decl., Gaia Coordinates; ϖ, Gaia parallax; m G ,Gaia G-band magnitude; B p − R p , Gaia G BP − G RP color; M G , Gaia G-band absolute magnitude; L X , 0.2-12 keV X-ray luminosity; HR, 2-12 to 1-2 keV hardness ratio.

Table 1
Parameters of the UV-selected SySt Candidates within 500 pc

Table 2
Parameters of X-Ray Counterparts of G500AGBs within 500 pc